Trump meets Ukrainian leader amid Russia investigation

[...] the two presidents posed for photographs in the Oval Office and made brief remarks following Poroshenko's more extensive meetings with Vice President Mike Pence and the administration's top national security advisers.

Trump has maintained that he hopes to establish better ties with Moscow, repairing ill will from the Obama era that resulted from Russia's 2014 annexation of Ukraine's Crimea region and its widely condemned support of Syria's President Bashar Assad, despite his attacks against civilians.

In April, following a suspected chemical attack against civilians in northern Syria by government forces, Trump said U.S. relations with Russia "may be at all-time low."

Trump has also raised concerns among NATO allies about whether he would turn his back on the military alliance, which partly promises U.S. support for European allies against Russian aggression.

In his meeting later with Defense Secretary Jim Mattis, Poroshenko said, "I think that we can expand our cooperation because we fight not only for our territorial integrity and our independence, not only for our sovereignty, we are fighting for freedom, we are fighting for democracy."

The White House meeting began shortly after the Trump administration announced it has imposed sanctions on two Russian officials and three dozen other individuals and companies over Russian activities in Ukraine.