Republican Greg Abbott said he had allocated $1bn (£706m) in state funds to uphold border security.

“While securing the border is the federal government’s responsibility, Texas will not sit idly by as this crisis grows,” Mr Abbott said.

One of President Joe Biden’s first acts in office was to end border wall construction.

In February, the Democrat rolled back the emergency order used to fund his predecessor Donald Trump’s Mexico border wall – a key symbol of the former president’s agenda – and said no further tax dollars would be spent on it.

It’s not clear if Mr Abbott has the authority to order a wall in Texas independently.

“It will help all of us to work on ways to stem the flow of unlawful immigration and to stem the flow of illegal contraband,” the governor told a press conference on Thursday.

But the plan is likely to face legal challenges.

The American Civil Liberties Union of Texas called it “an attempt to distract from his governing failures while targeting vulnerable immigrants”.

This month, the number of undocumented immigrants reaching the US-Mexico border hit its highest level in more than 20 years.

US Customs and Border Protection said it had apprehended 180,034 migrants, mostly single adults, in May – the highest monthly total since April 2000. The majority are fleeing poverty and violence in Central American countries like Guatemala.

A pandemic emergency rule known as Title 42 allows border agents to turn away most single adults and many families.

However, it does not apply to unaccompanied children. Thousands have crossed the border and are being held in US immigration detention facilities.

Tensions have been mounting between the Biden administration and Mr Abbott, whose state is an epicentre of illegal crossings.

Justice Department officials threatened to sue Texas after the governor ordered child-care regulators to cancel the licences of centres that shelter immigrant children.

On Thursday, Mr Abbott blamed the rise in migrant crossings on Mr Biden’s policies, saying he hoped to give more details about the wall next week.

“Some of these border barriers will be built immediately,” he added.

Building a southern border wall was a signature pledge of Mr Trump’s 2016 presidential campaign. He initially insisted Mexico would pay for the wall – which it declined to do. By the time Mr Trump left office, the US had spent about $15bn (£11bn) on the project.

According to the New York Times, the Trump administration built more than 450 miles of new wall, most of it in areas which had older barriers already. Much of this was in Arizona rather than Texas, where some landowners took legal action to resist construction on their properties.

Mr Biden promised a more humane immigration agenda, declaring in a presidential debate that the separation of children from their parents under the Trump administration’s zero-tolerance policy was “criminal”.

He has launched a task force to reunite separated migrant families, and repealed Mr Trump’s “Remain in Mexico” policy, which required US asylum seekers to wait in Mexico while their applications were processed.

Republicans have blamed Mr Biden’s policies for the border surge, however – as has Guatemala’s President Alejandro Giammattei.

Before meeting US Vice-President Kamala Harris this week, he told CBS News that after Mr Biden took office, “the very next day the coyotes were here organising groups of children to take them to the United States”.

During her visit, designed to address the root causes of immigration, Ms Harris told illegal immigrants thinking of making the trek to America: “Do not come.”

Police in Nicaragua have detained five more prominent opposition figures, in what critics say is a crackdown on opponents of the country’s president.

Several former allies of long-time President Daniel Ortega were among those arrested on Sunday.

Police accused them of inciting foreign interference in Nicaragua’s affairs, among other crimes.

About 12 opposition figures, including four hopefuls in November’s election, have been arrested in recent days.

Mr Ortega, 75, is expected to seek a fourth consecutive term in November’s presidential election. But opinion polls suggest his popularity has plummeted after a violent crackdown on anti-government protests in 2018 in which hundreds of people were killed.

In power since 2007, Mr Ortega has been accused of suppressing dissent and political opposition to his rule ahead of the poll.

The police said those held on Sunday were all members of Unamos, an opposition party that is largely made up of dissidents who split from President Ortega’s ruling party, the Sandinista National Liberation Front (FSLN).

The FSLN was a socialist revolutionary movement that swept to power in the Central American nation in 1979.

Among those detained were former Sandinista Health Minister Dora Tellez and retired General Hugo Torres, who fought with Mr Ortega against dictator Anastasio Somoza in the 1970s.

Mr Torres said the opposition would keep fighting against Mr Ortega.

“These are desperate moves by a regime that feels it is moribund, that has no legal standing, that has no justification… to remain in power beyond November of this year when free and supervised elections should be held,” Mr Torres said.

Julie Chung, the top US diplomat for Latin America, called the arrests “arbitrary” and denounced Mr Ortega’s “campaign of terror” in a tweet.

Nearly all of those detained have been accused of plotting against Nicaragua’s sovereignty and independence and of organising terrorist acts with financial help from foreign powers.

They have been held under a controversial treason law passed in December by Nicaragua’s National Assembly, which is dominated by government allies.

Under the law, the government has the power to ban candidates from running for office if they are deemed to be traitors to Nicaragua. Anyone designated a traitor can be sent to prison for up to 15 years.

The government says the law aims to protect “the independence, the sovereignty and self-determination” of Nicaragua. It says the country is under threat from imperialist powers in the US and “coup-mongers” within Nicaragua who are determined to overthrow President Ortega.

But critics say the law is designed to stop opposition politicians from standing in the election. The US, the UK and the EU have imposed sanctions on Nicaraguan officials, whom they accuse of undermining democracy.

Leaders of the major industrial nations have pledged one billion Covid vaccine doses to poor countries as a “big step towards vaccinating the world”, Boris Johnson has said.

At the end of the G7 summit in Cornwall, the PM said countries were rejecting “nationalistic approaches”.

He said vaccinating the world would show the benefits of the G7’s democratic values.

There was also a pledge to wipe out their contribution to climate change.

After the first meeting of world leaders in two years, Mr Johnson said “the world was looking to us to reject some of the selfish, nationalistic approaches that marred the initial global response to the pandemic and to channel all our diplomatic, economic and scientific might to defeating Covid for good”.

He said the G7 leaders had pledged to supply the vaccines to poor countries either directly or through the World Health Organization’s Covax scheme – including 100 million from the UK.

The communique issued by the summit pledges to “end the pandemic and prepare for the future by driving an intensified international effort, starting immediately, to vaccinate the world by getting as many safe vaccines to as many people as possible as fast as possible”.

It also includes steps to tackle climate change, with leaders re-committing to the target of reaching net zero greenhouse gas emissions by 2050 at the latest and pledging to eliminate most coal power.

Mr Johnson rejected suggestions the vaccines pledge was a moral failure by the G7 as it was not enough to cover the needs of poorer countries.

He referred to the the UK’s involvement in the development of the Oxford-AstraZeneca vaccine.

“Already of the 1.5 billion vaccines that have been distributed around the world, I think that people in this country should be very proud that half a billion of them are as a result of the actions taken by the UK government in doing that deal with the Oxford scientists and AstraZeneca to distribute it at cost,” he said.

He added that “we are going flat out and we are producing vaccines as fast as we can, and distributing them as fast as we can”.

The target to vaccinate the world by the end of next year would be met “very largely thanks to the efforts of the countries who have come here today”, Mr Johnson said.

The leaders slightly exceeded their target of donating a billion Covid vaccines to poorer countries within the next year, if funding for future doses is included alongside individual jabs.

There was also a commitment to build the frameworks to prevent and fight future pandemics. Elsewhere in the 25-page communique, there were several references to China, which President Biden said was a change from previous meetings of the world’s advanced economies.

Pledges made this time included working together to respond to China’s impact on world trade.

On the recovery from Covid there was even a reference to Prime Minister Boris Johnson’s trademark domestic policy – the need to reduce inequalities by “levelling up”.

Charities and campaigners issued statements calling out vague promises and missed opportunities, but Mr Johnson will feel that post-Brexit Britain has staged a diplomatic show that was both competent and confident.

Mr Johnson also dismissed the suggestion that patents for vaccines should be waived in order to boost global supply, something which the US backed last month.

He said he wanted to protect “incentives for innovation” while building up manufacturing capacity, especially in Africa.

Elsewhere in their communique, G7 leaders also pledged to:

The communique calls for a “timely, transparent, expert-led, and science-based WHO-convened” investigation into the origins of Covid-19.

US President Joe Biden has previously said the US intelligence community is split on whether coronavirus came from human contact with an infected animal or from a lab accident – a theory rejected by China.

Mr Johnson said “the advice that we’ve had is it doesn’t look as though this particular disease of zoonotic origin came from a lab”, but he added: “Clearly anybody sensible would want to keep an open mind about that”.

French President Emmanuel Macron said the international community needed clarity about the origins of the virus but said it was up to the WHO to investigate.

With G7 countries accounting for 20% of carbon emissions, Mr Johnson said: “We were clear this weekend that action needs to start with us.”

But pressed on the lack of binding agreements and timetables, the prime minister says he will not “pretend our work is done” and he will be “on everybody’s case” to make further progress ahead of the COP26 summit in Scotland later this year.

Kirsty McNeill from Crack the Crises, a coalition of charities and NGOs including Save the Children and Oxfam, said the G7 summit was a “historic missed opportunity” on Covid-19 and climate change.

Leaders arrived “with good intentions but without their cheque books”, she said.

Joanna Rea, from Unicef UK, said the G7 pledge on vaccines was “the beginning of the action required to end this pandemic” but called for a “rapid acceleration of dose sharing in the next three months to ensure millions of vaccines get to the people in countries who need them the most”.