New British foreign minister and lead Brexit campaigner Boris Johnson urged the EU Monday to leave its doors open on strategic issues and promised Britain would continue to play a "leading role" in Europe.

Meeting his EU peers in Brussels for the first time since his shock appointment, the normally ebullient Johnson was on his best behaviour after infuriating them in the Brexit run-up by comparing EU ambitions for closer integration to Adolf Hitler's.

He told reporters after "a long productive day" that while the government would press ahead with leaving the 28-nation club, "that in no sense means the end of Britain's part in Europe."

This would be especially true in foreign policy, and London saw no reason to fear EU efforts to develop a more active global role as championed by bloc foreign policy chief Federica Mogherini, he said.

"We are very keen to see the EU develop and go forward," he said.

"What we would say is to make sure that there are kinds of docking stations and doorways open for further UK involvement down the track."

US Secretary of State John Kerry, attending his first EU foreign ministers meeting in a high level gesture of solidarity with the EU, said Johnson had told his peers Britain intended to remain a "vital component" of Europe.

The prospect of Britain leaving has stoked fears the bloc could struggle to establish a global role since it will be losing a nuclear-armed power with a permanent, veto-wielding seat on the UN Security Council.

Britain's parliament was due to vote later Monday on replacing the country's ageing Trident nuclear deterrent, a massive commitment costing £41 billion (49 billion euros, $54 billion).

The foreign ministers' meeting was overshadowed by the failed military coup in Turkey and last week's deadly attack in Nice, the third major terror incident in France since 2015.

Johnson said they discussed both issues, offering support for France and trying to balance backing for the Turkish government against the need for it to uphold EU democratic and rule of law norms in the coup aftermath.

The new foreign secretary was a key player in the June 23 Brexit referendum.

His appointment stunned many in Europe, with French Foreign Minister Jean-Marc Ayrault saying he had lied to voters during the campaign.

"There are lots of things to work on with Britain. I will always talk to Boris Johnson with the greatest sincerity, the greatest frankness, I think it's like that we have to move on," Ayrault said.

Asked if Johnson had apologised over his comparision of the EU with Hitler, Ayrault said the Briton had not, but like other ministers Johnson knew well "that Europe represents the (best) chance for freedom and democracy."

Johnson held bilateral meetings with Mogherini and the foreign ministers of 19 EU countries including Germany and France.

Johnson's visit caused some trepidation given his reputation for quips which have often landed him in hot water.

The former mayor of London and one-time schoolmate of former prime minister David Cameron is well known in Brussels where he worked in the 1990s as the Daily Telegraph's EU correspondent.

His critics say he routinely exaggerated or skewed his stories to play to the eurosceptic gallery at home.

Officials in Brussels stressed they would welcome Johnson but there is little doubt his Brexit role ruffled feathers.

Johnson was supposed to have met all his EU colleagues on Sunday for an informal dinner but several member states objected, saying it would amount to "informal talks" with London before it began formal divorce negotiations, one European diplomat said.