When Ukraine successfully targeted Russia's prized warship last month with anti-ship cruise missiles, it had some help from the United States.
Ukrainian forces, having spotted the Russian warship in the Black Sea, called their American contacts for confirmation that it was in fact the Moskva, sources familiar with the events told CNN.
The US responded that it was, and provided intelligence about its location.
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It is not clear whether the US knew Ukraine would move to strike the ship, however, and the US was not involved in that decision, the sources said.
"We routinely and have now for weeks been sharing information and intelligence about Russian units, both at sea and ashore, to help the Ukrainians defend themselves against this invasion. And we're going to continue to do that," Pentagon press secretary John Kirby told CNN's Brianna Keilar on "New Day" Friday and reiterated his earlier statement.
Kirby had previously told CNN: "We did not provide Ukraine with specific targeting information for the Moskva. We were not involved in the Ukrainians' decision to strike the ship or in the operation they carried out. We had no prior knowledge of Ukraine's intent to target the ship. The Ukrainians have their own intelligence capabilities to track and target Russian naval vessels, as they did in this case."
Asked Friday if US intelligence has resulted in Russian deaths, Kirby said, "I am not going to get into the specifics about the intelligence that we provide."
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He added: "The intelligence that we provide to Ukraine is legal, it's lawful, it is legitimate, and it is limited. And we're very careful about what we share and when we share it."
The ship sank after it was struck by two Ukrainian cruise missiles on April 14, dealing a huge blow to the Russian military.
The episode, first reported by NBC News, reflects the Biden administration's increasingly forward-leaning posture when it comes to sharing intelligence with Ukraine, part of a broader policy shift toward helping Ukraine defeat Russia decisively on the battlefield and significantly weaken its military.
But it also raises questions about what the red lines are for the US and Russia when it comes to US military support to Ukraine.
The US has for months provided Ukrainian forces with intelligence about Russian troop movements inside Ukraine, including intercepted communications about Russian military planning.
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It also provides Ukraine with maritime awareness information to allow the country to better understand the threat posed by Russian ships in the Black Sea, many of which are firing missiles onto Ukrainian territory.
There are also clear limits, however, to what the US will share, multiple sources told CNN.
For example, the US has so far declined to provide information to Ukraine about potential targets inside Russia itself.
And while the intelligence the US shares about Russian troop movements inside Ukraine can include details like vehicles and types of personnel at a particular location, the US has not provided Ukraine with intelligence about specific Russian military leaders' whereabouts, officials have said.
"We do not provide intelligence on the location of senior military leaders on the battlefield or participate in the targeting decisions of the Ukrainian military," Pentagon press secretary John Kirby told reporters on Thursday.
Kirby added that "Ukraine combines information that we and other partners provide with the intelligence that they themselves are gathering on the battlefield, and then they make their own decisions, and they take their own actions."
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Following a series of military and logistical setbacks, Moscow has most recently concentrated efforts on the Donbas region of eastern Ukraine, which has been on the front line of the Russia-Ukraine conflict since 2014.
Heavy fighting continued on Thursday inside the Azovstal steel complex, according to Lt. Col. Denys Prokopenko, a Ukrainian commander at the plant.
He claimed the Russians had broken their pledge to allow civilians to leave through evacuation corridors Thursday.
There are thought to be between 200 and 300 civilians still inside the plant, including 30 children.
Since Sunday, it has been bombarded from land, sea and air.
"For two days now, the enemy has broken into the territory of the plant. There are heavy, bloody battles," Prokopenko said.
