President Donald Trump pressedthe North Atlantic Treaty Organizations 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 a readout of the call released by the White House.

During a call on Sunday with Secretary General Jens Stoltenberg, Trump agreed to join in 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.

Photographer: Armend Nimani/AFP via Getty Images

Intense fighting has taken place between government troops and pro-Russian separatists near Ukraines Russian border during the past week, the latest episode in a crisis that began when Russia annexed Crimea in March 2014.

Trump has repeatedly questioned the value of NATO, the military alliance forged in 1949 as the cornerstone of the Wests defense, which he has referred to as obsolete.

Hes recently adopted a more conciliatory tone. Trump called the alliance very important in an interview in January, and U.K. Prime Minister Theresa May said Trump was 100 percent behind NATO after their January meeting in Washington.

The U.K. provides the second-largest contribution to NATO, after the U.S. While the alliance agreed since 2014 that its members should spend 2 percent of gross domestic product on defense, few of its 28 members do, and Trump has demanded that member nations to pay their fair share toward its costs.

NATO was established after World War II to protect western democracies against the Soviet Union. A key tenet is that an attack on any alliance member is considered an attack on all. And thats what Trump has questioned.

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The parties agreed to continue close coordination and cooperation to address the full range of security challenges facing NATO, the readout of the call with Stoltenberg said.

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Trump Speaks of 'Strong Support' for NATO in Call With Leader - Bloomberg