Russia is threatening to reject President Donald Trump's Ukraine peace plan unless "key understandings" from his Alaska summit with President Putin are upheld.

Russian Foreign Minister Sergei Lavrov said on Tuesday that an amended peace plan for Ukraine must reflect the "spirit and letter" of understandings reached between President Vladimir Putin and U.S. President Donald Trump at their Alaska summit.

The U.S. Army secretary, Daniel P. Driscoll, is in the United Arab Emirates for scheduled meetings with a Russian delegation about President Trump’s latest plan for peace in Ukraine, a U.S. official said.

Polish Prime Minister Donald Tusk said “it would be good to know for sure who is the author of the plan,” as tensions over elements that mirror long-standing Russian demands.

President Volodymyr Zelenskyy said Friday that Ukraine has to confront the possibility of losing its dignity or risking the loss of a key partner as it figures out how to respond to a U.S. peace proposal to end Russia's war with his country.

Washington and Kyiv said that “highly productive” discussions over a proposal to end the war with Russia would continue. But details remained unclear.