Kerry and Johnson show united front in London

US Secretary of State John Kerry and British Foreign Secretary Boris Johnson held a joint press conference Tuesday after their first meeting in London. The two countries' top diplomats insisted that the so-called "special relationship" between the US and the UK would continue, and that Britain's role on the world stage would not be diminished despite Britain's vote last month leave the European Union.

The so-called Brexit vote, which was opposed by then-Prime Minister David Cameron, compelled Cameron to resign. The loquacious Johnson became the face of the Brexit movement and was a prime contender to replace Cameron.

But a power struggle inside the Conservative Party left Johnson with the consolation prize of foreign minister, surprising many observers. Former Home Secretary Theresa May ascended to 10 Downing Street.

Beyond talk of the future of Britain's global status they discussed a range of issues including Syria, Yemen, Ukraine and the Islamic State.

After meeting May, Kerry thanked the prime minister for her "very pronounced commitment to living up to the special relationship between the United States and the United Kingdom."

His bilateral meetings with the new British leaders were not just introductions but precursors to multilateral meetings with European Union ministers later in the day regarding the civil war in Syria, and a meeting with Arab leaders regarding the conflict in Yemen.

Johnson maintained that Britain would not shrink from the world stage, insisting that it would become "an even greater global power…more outward, more active on the global stage than ever before."

But he did an about-face on Syria, saying its leader Bashar al-Assad had to go.

That is the stated goal in Washington, Brussels and London, but Johnson wrote a newspaper column in March titled "Bravo for Assad," in which he credited the Syrian strongman with saving the ancient city of Palmyra, a UNESCO World Heritage site, from IS militants.

"No matter how repulsive the Assad regime may be - and it is - their opponents in Islamic State ...are far, far worse," Johnson wrote in London's Daily Telegraph newspaper.

Johnson falls in line

But Tuesday, as foreign secretary before a room full of journalists, with the US secretary of state at his side, Johnson changed his tune, saying Assad had to go.

"The situation on the ground in Syria is dire," he told journalists. "Aleppo, a city of 300,000 is besieged and the access route for humanitarian aid is cut off."

He called on Russia and Iran to open access to the areas under siege. And, he added, "The whole country is facing a humanitarian catastrophe."

Kerry seemed to make a veiled call for the United Kingdom to stay together. Without mentioning Scotland, which is seriously considering a possible exit from the UK in order to stay part of the EU, the US secretary noted that Prime Minister May was committed to all UK citizens.

"One thing that also struck me was her commitment to the precious bond of citizens and communities and citizens of this country," Kerry said. "That is reassuring and important."

While the US would have preferred Britain to remain part of the EU - President Barack Obama said as much during a visit to Britain in the spring - Kerry stressed the importance of the US-British relationship regardless of whether the island nation is an EU member.

"Winston Churchill told the US Congress there's almost nothing that can't be achieved when Britain and America work heart in hand," Kerry recalled.

He added, "This is a different time and it requires different thinking."