U.S. President Donald Trump said Monday that his upcoming meeting with Russian President Vladimir Putin on Friday in Alaska will be a "feel-out meeting."

Speaking at a White House press conference, Trump said a future meeting could also involve Ukrainian President Volodymyr Zelensky, or include both the Russian and Ukrainian leaders.

A White House official told reporters on Saturday that Trump remained open to a summit with both leaders.

U.S. Ambassador to NATO Matthew Whitaker said Sunday it was still possible that Zelensky could attend Friday's meeting in Alaska.

"The decision is going to be made by President Trump," Whitaker said. "There's still time to make that decision."