WASHINGTON (AFP) - Nato is the "bulwark of international peace and security" but its European members "must pay what they owe," US President Donald Trump said on Wednesday (April 12) alongside the political head of the military alliance.

Reversing some of his campaign rhetoric, Trump told a joint news conference that Nato "is no longer obsolete" and hailed its role in the fight "against terrorism."

But he renewed his argument that Nato's member states need to dedicate 2 per cent of their gross domestic product to military expenditure.

"In facing our common challenges, we must also ensure that Nato members meet their financial obligations and pay what they owe," he said.

Nato Secretary-General Jens Stoltenberg said he and Trump had agreed in their talk that "Nato is a bedrock of security, both for Europe and for the United States... and therefore I welcome the very strong commitment of the United States to the security of Europe."

Increased concerns among Nato's European states about Russian military activity on its eastern flank fed into a question to Trump about strained ties with Russia.

Trump replied that "it would be wonderful... if Nato and our country could get along with Russia."

He said "we may be at an all-time low in terms of our relationship with Russia," but said it would be "a fantastic thing" if the relationship could improve with Russian President Vladimir Putin.