NEW YORK (AP) — Russian leader Vladimir Putin agreed at his summit with President Donald Trump that the United States and its European allies could offer Ukraine a security guarantee resembling NATO’s collective defense mandate as part of an eventual deal to end the war, a U.S. official said Sunday.

Trump envoy Steve Witkoff, who took part in the talks Friday at a military base in Alaska, said it “was the first time we had ever heard the Russians agree to that” and called it “game-changing.”

“We were able to win the following concession: That the United States could offer Article 5-like protection, which is one of the real reasons why Ukraine wants to be in NATO,” Witkoff told CNN’s “State of the Union.”

Witkoff offered few details on how such an arrangement would work. But it appeared to be a major shift for Putin and could serve as a workaround to his deep-seated objection to Ukraine’s potential NATO membership, a step that Kyiv has long sought.