In an interview Sunday on ABC News' "This Week," Sen. Amy Klobuchar threw her support behind Ukrainian President Volodymyr Zelenskyy after the volatile White House meeting with President Donald Trump.

The Minnesota Democrat said she was "appalled by what happened in the Oval Office," and thinks the fallout of the exchange "is not in President Trump's best interest."

"We stand with our friends, not our enemies," Klobuchar said. "The great country of America goes into negotiations with strength, not surrender."

Meanwhile, British ambassador to the U.S. Lord Peter Mandelson said the U.S.-Ukraine relationship needs a "reset" after the Trump-Zelenskyy meeting.

"I think that Ukraine should be the first to commit to a ceasefire and defy the Russians to follow," Mandelson told "This Week" co-anchor George Stephanopoulos. "And then, as part of the unfolding plan for this negotiation, the Europeans and perhaps some other countries too, have got to consider how they are going to put forces on the ground to play their part in providing enduring security and deterrence for Ukraine."

This is a developing story. Please check back for updates.