His comments come shortly after the U.S. and Ukraine signed a minerals deal, an agreement that Vance said showed the White House is making progress.

What’s emerged from the Washington-led effort to end the war in Ukraine suggests a deal that seems likely to be favorable to Russia.

Ukraine's Air Force lost a Su-27 fighter jet during a Russian aerial attack on April 28. The aircraft was conducting a combat mission, supporting ground troops. The loss follows the earlier downing of the second F-16 fighter jet, which reportedly occurred in the Russia-bordering northeastern region of Sumy on April 16.