Washington – President Donald Trump pressed the North Atlantic Treaty Organization’s general secretary on how to encourage member nations to pay more for their defense while expressing “strong support” from the U.S. for the alliance, according to readout of the call released by the White House.

Ina call on Sunday with Secretary General Jens Stoltenberg, Trump agreed to join a meeting of NATO leaders in late May and discussed the potential for “a peaceful resolution of the conflict along the Ukranian border,” according to the readout.

Over the past week a flare-up in hostilities has erupted between the Ukrainian military and Russia-backed separatists, with each accusing the other of a new wave of shelling. More than 40 people have been killed in both government and rebel-held areas.

Trump was elected on a pledge to push NATO members to increase their funding to the western alliance to ease the financial burden on the United States.

This proposal has drawn opposition from both his fellow Republicans as well as Democrats and the idea has worried European allies who fear Russian President Vladimir Putin might take advantage.

The U.S. President has drawn fire at home for wanting to warm up ties with Putin.

In an interview-broadcast on Sunday during Fox Channel’s Super Bowl pre-game show, Trump waved off concern from interviewer Bill O’Reilly that “Putin is a killer.”

“We’ve got a lot of killers…You think our country’s so innocent? You think our country’s so innocent?” Trump said, citing the 2003 war in Iraq.