Ties between Washington and London will stay "special and unbreakable" after Britain leaves the European Union, US Secretary of State John Kerry said after meeting British leaders on Tuesday.
Kerry said he was "gratified by the reassurance" he heard on Britain's post-Brexit plans from Prime Minister Theresa May and Foreign Secretary Boris Johnson.
"I am convinced that this UK government intends to lead as strongly as possible in NATO," Kerry said at a joint press conference with Johnson, adding that he also expected Britain to continue to play leading roles at the United Nations and in the fight against Islamic State.
Kerry and Johnson were scheduled to join the foreign ministers of Germany, France and Italy to discuss Syria later Tuesday.
They also planned to discuss Yemen over dinner with the foreign ministers of Saudi Arabia and the United Arab Emirates.
Johnson promised that Britain will become "more active, more outward facing" after Brexit.
He declined to apologize for past remarks referring to US President Barack Obama's "part-Kenyan ancestry" or likening former secretary of state Hillary Clinton to a "sadistic nurse."
"We could spend an awful lot of time going over lots of stuff that I've written over the last 30 years ... but there are some serious issues before us," Johnson said when asked about his past remarks.
He was also pressed on whether he had changed his position on Syria, after he argued in December that Western powers should cooperate with President Bashar al-Assad and Russian President Vladimir Putin to find a solution to the Syrian conflict and subdue Islamic State forces.
"It's always been my view that he (al-Assad) should go," Johnson said.
He said Syria had become "hellish ... and it is very hard to see a way through."
But a solution "must involve the regime engaging in some kind of peace process," Johnson said.
"The current situation on the ground in Syria is dire," he said.
He said a political solution was also "the only way forward" in Yemen.
Kerry met May at her official London residence on Tuesday, holding "substantive discussion about the US-UK special relationship" and the importance of Washington and London's "strong partnership," State Department spokesman John Kirby said on Twitter.