WASHINGTON — The White House rejected on Friday a Vladimir Putin-backed effort to hold a referendum in eastern Ukraine on the region’s future, distancing itself from the idea in the aftermath of President Donald Trump’s controversial summit with the Russian leader.

Russia’s ambassador to the U.S., Anatoly Antonov, said the two leaders had discussed the possibility of a referendum in separatist-leaning eastern Ukraine during their Helsinki summit.

But Trump’s National Security Council spokesman Garrett Marquis said agreements between Russia and the Ukrainian government for resolving the conflict in the Donbas region do not include any such option and any effort to organize a “so-called referendum” would have “no legitimacy.”

The back-and-forth came as the White House outlined the agenda for a proposed second summit between Trump and Putin — in Washington this fall — that would focus on national security. Moscow signaled its openness to a second formal meeting between the two leaders as criticism of Trump over his first major session with his Russian counterpart kept up in the U.S.