London, Dec 3 (AP) President Donald Trump barreled into a NATO leaders' meeting on Tuesday aiming insults at French President Emmanuel Macron, slamming '"unpatriotic" Democrats at home for holding an impeachment hearing while he is abroad and playing down the impact his domestic troubles are having on his standing on the global stage.

Trump began his first of two days at the NATO conference by harshly rebuking Macron, once arguably his closest ally among foreign leaders, for recently saying NATO was experiencing "brain death" as a result of diminished US leadership in the alliance under Trump.

Before meeting with Macron on the sidelines of the meeting, Trump laced into the French president for what he said were "very, very nasty" comments.

"I think that's insulting to a lot of different forces," Trump said.

"You just can't go around making statements like that about NATO. It's very disrespectful."

Hours after the broadside, Macron and Trump sat side by side for a one-on-one meeting.

Macron said he stood by his comments about the health of the NATO alliance.

He also firmly expressed his frustration that Trump withdrew hundreds of American troops from Syria in October.

The decision by Trump, made without consulting NATO allies, gave Turkey, another NATO member, a green light to launch operations against Syrian Kurdish forces who played a key role in the fight to clear a huge swath of Syria of the Islamic State.

Trump and Macron have had an up-and-down relationship in the nearly three years Trump's been in office.

Macron, who early in Trump's presidency had looked to cultivate a close relationship with Trump, hosted Trump in France in 2017 for Bastille Day celebrations in Paris. Trump reciprocated by honoring Macron last year with the first state visit of a foreign leader during his time in the White House.

But the relationship has been put under new stress in the aftermath of Trump pulling out US troops from Syria without coordinating with France and other NATO allies.

As they answered questions from reporters, the chasm between Trump and Macron was most apparent as they discussed their concerns over Turkey's plan to purchase an anti-aircraft system from Russia.

Macron said there is a disconnect in allowing Turkey to buy an anti-aircraft S-400 missile system from Russia and also be a NATO member.

Trump said he is weighing issuing sanctions against Ankara if they move forward with plans to buy the weapons.

Ahead of the meeting, President Recep Tayyip Erdogan said he would oppose a NATO plan to defend the Baltic region if the alliance does not back Turkey over its fight against Kurdish groups it considers terrorists.

"I'm sorry to say we don't have the same definition of terrorism around the table," Macron said in a swipe at Turkey.

Trump showed a measure of deference to Erdogan, noting that Turkey was "very helpful" during an October US special commando raid that lead to the death IS leader Abu Bakr al-Baghdadi near Syria-Turkey border.

"We flew over areas that was totally controlled by Turkey and Turkish military,” Trump said.

"They were very supportive actually. We didn't tell them what we were doing or where we were going. Turkey could not have been nicer, could not have been more supportive."

Trump criticised Democrats at the outset Tuesday, calling the impeachment push by his political rivals "unpatriotic" and "a bad thing for our country."

Trump, who initially commented while meeting with NATO Secretary-General Jens Stoltenberg, is upset that Democrats scheduled an impeachment hearing while he is abroad.

The House Judiciary Committee has set a hearing on the constitutional grounds for Trump's possible impeachment on Wednesday just before the NATO summit concludes.

"I think it's very unpatriotic of the Democrats to put on a performance," Trump said.

"I think it's a bad thing for our country."

Trump insists he's solely focused on scoring domestic and foreign policy wins, including making NATO members spend more on defense. But he's often appeared consumed by the day-to-day battle against impeachment.

"I'm not even thinking about it," Trump insisted anew Tuesday.

Before the trip to London, Trump slammed "Do Nothing Democrats" for scheduling the hearing during the NATO meeting as "Not nice!"

He also said that, during the flight, he had read a newly issued Republican-prepared report on impeachment that called his decision to hold up military aid to Ukraine "entirely prudent." (AP)

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