CAMP DAVID, Maryland, July 31 (Reuters) - President Donald Trump said on Friday that the United States has not agreed to ​Ukraine building Patriot missiles but that talks are ongoing, adding that the U.S. ‌must be "very careful about letting somebody build them."

Trump said during a meeting with Ukrainian President Volodymyr Zelenskiy in Turkey this month that he was going to give Ukraine a license to manufacture Patriot missile interceptors ​to help defend against Russian strikes, but has since backed away from that pledge ​despite hosting Zelenskiy at the White House this week.

Asked about the Patriot missiles ⁠during a cabinet meeting at the Camp David retreat on Friday, Trump emphasized concerns about ​sharing advanced U.S. weaponry including missile technology.

"It's a big step," Trump said.

"In the case of President ​Zelenskiy, he'd like to have some Patriots, he'd like to have some Tomahawks, which are you know lethal — one offensive, one defensive," Trump said.

"You have to be very judicious, but you have to be very ​careful. Now we have not agreed to that. We're talking about it, but it's a ​hard thing to give away that kind of technology. And I don't think this would ever happen but, ‌you ⁠know, there's people that you give that technology, they can someday turn on you," Trump said.

As Russia has stepped up its air attacks, Ukraine has run chronically low on supplies of Patriots, which remain the only weapon in its arsenal capable of downing ballistic missiles.

Ukraine has long sought ​a co-production agreement for ​the Patriot PAC-3 missiles ⁠to intercept ballistic missiles, with an eye to building them domestically.

Trump's earlier pledge to provide a license for such a production agreement caught ​many by surprise, and Ukrainian officials have been meeting with Pentagon ​officials and ⁠industry executives since to work out firmer details.

Those efforts are continuing, but Ukrainian ambassador Olha Stefanishyna on Thursday said she is confident that Lockheed Martin, maker of the PAC-3 missiles, was fully committed to ⁠deepening ​cooperation with Ukraine. Lockheed executives met with Zelenskiy on Tuesday, ​and the company is planning to send executives to Ukraine soon, she said.