President Donald Trump on Friday said the U.S. "has not agreed" to grant Ukraine licenses to produce Patriot missile systems, apparently backtracking on one of Kyiv's top priorities in its war against Russia.

The advanced military technology is "a hard thing to give away," Trump said at a Cabinet meeting at Camp David, adding that a country that receives it could "someday turn on you."

"You have to be very careful," Trump said. He said the U.S. and Ukraine are still "talking about it."

Trump's latest comments on the war in eastern Europe came three days after he spoke at the White House with Ukrainian President Volodymyr Zelenskyy, who said the leaders had a "good meeting" about the Patriot licenses.

Trump's apparent shift also came amid growing concerns that the U.S. is burning through its stockpiles of top weaponry, including Patriots, as it continues to wage war in Iran, with air defenses being key to stopping Iranian missiles.

Less than three weeks earlier, Trump told Zelenskyy directly that the U.S. would grant his wish. "We're going to give a license to you to make Patriots," Trump said at the NATO Summit — though he added, "we haven't informed the company of that yet," possibly referring to defense contractors Lockheed Martin or RTX, both of which manufacture the missile systems.

But on Thursday, Trump told the Financial Times he was "not sure" if he would follow through on letting Kyiv build the "extraordinary weapon."

Ukraine's U.S. embassy did not immediately respond to CNBC's request for comment on Trump's latest remarks.

Zelenskyy says the Patriot system is crucial to Ukraine's ability to intercept incoming ballistic missiles from Russia. But even if Ukraine gets the go-ahead to begin manufacturing Patriots, it may still be years before any of the expensive, highly complex weapons are actually produced there.

The issue nevertheless "remains a top priority" for Kyiv, Zelenskyy said Friday following a call with Vice President JD Vance.

"We agreed that our teams will stay in touch and work through everything discussed today," Zelenskyy wrote in an X post. "I thank the United States for its support of Ukraine and our people."

Zelenskyy later said he met with Lockheed's team to discuss "our joint capabilities related to Patriots and other systems."

"Our teams are already working on specific solutions to move to co-production as quickly as possible and increase our capabilities to protect lives," he said.

Lockheed and RTX did not immediately respond to CNBC's requests for comment.