By David Morgan and Jeff Mason WASHINGTON (Reuters) -Top Republicans aligned with U.S. President Donald Trump pushed Ukrainian President Volodymyr Zelenskiy on Sunday to change his position on the war with Russia or step aside,

Following Trump's lead, White House officials and Republicans in Congress used news show appearances to demand that Zelenskyy display more gratitude for U.S. support and an openness to potential war-ending concessions to Russian President Vladimir Putin.

President Volodymyr Zelenskiy said on Monday that Ukraine had to engage in "substantive" diplomacy to bring to a rapid end the three-year-old war with Russia, and he hoped to be able to rely on U.S. support in securing peace.

"Even while Russia talks about peace, they are continuing their relentless aggression," Starmer said at the meeting.