US President Donald Trump  launched a scathing attack on French counterpart Emmanuel Macron for his remarks on Nato as the alliance met in London to mark its 70th anniversary.

In a joint press conference with Nato Secretary General Jens Stoltenberg on Tuesday Trump called Macron's 'brain dead' assessment of the military coalition "very insulting" and a "very dangerous statement" to make.

"Nobody needs Nato more than France," he added.

Denying that Washington's partnership with Nato was becoming tenuous, Trump said: "I do see France breaking off ... I see him breaking off."

Macron, in a controversial interview, told The Economist magazine last month: "What we are currently experiencing is the brain death of Nato."

The 41-year-old warned that the coalition was standing on "the edge of a precipice" and should start thinking strategically as a geopolitical power.

He had appeared to cast doubt on the Nato principle that an attack on a member would be deemed as an attack on the rest.

However the two men later met for talks and addressed the media, with Macron standing by his comments about Nato and both appearing to be in agreement on the need for changes to Nato funding levels:

^{The US and French presidents held a joint media conference after their talks}

Trump had earlier also trained his guns on "delinquent" alliance members who fail to contribute their proper share to the alliance's budget. 

"When I came in, I was angry at Nato, and now I've raised $130 billion," Trump said as he alluded to the figure Stoltenberg promised European members and Canada would contribute by next year.

"And yet you still have many delinquent -- you know I call them delinquent when they're not paid up in full," he added.

Trump has been urging member-states to keep to their pledge of increasing contributions by two percent of gross domestic product by 2024. 

He was particularly critical of Germany, spending only one to 1.3 percent of its GDP.

Leaders of 29 Nato member-states are arriving in the British capital for a two-day meet to discuss new threats and to iron out differences.

In sign of what's to come, Turkish President Recep Tayyip Erdogan said that he would oppose a plan to defend Baltic countries unless Nato labels the Syrian Kurdish People's Protection Units (YPG) as terrorists.

Some Nato members have condemned Ankara's military operation in Syria to take on the Kurdish militant group.

Before leaving for London, Erdogan said he had spoken to Polish President Andrzej Duda on the phone and will meet leaders of Baltic countries to discuss the defense plan.

"With pleasure, we can come together and discuss these issues there as well," he said.

"But if our friends at Nato do not recognize as terrorist organizations those we consider terrorist organizations ... we will stand against any step that will be taken there."