British PM Theresa May hosts John Kerry at Downing Street

London (AFP) - US Secretary of State John Kerry on Tuesday became the first senior foreign official to meet British Prime Minister Theresa May since she took office after the Brexit referendum.

Kerry visited May at her Downing Street office on the last day of a five-stop tour of European capitals, ahead of talks with the British, German, French and Italian foreign ministers on the conflict on Syria.

Washington was dismayed by last month's British vote to leave the European Union, seeing the June 23 referendum result as a blow to Western unity and to the world economy.

But both Kerry and US President Barack Obama have vowed that the "special relationship" between Britain and the United States will remain strong, and Kerry and May were all smiles as they met.

Kerry banged his head on the famous black door of the British leader's 10 Downing Street residence as he turned to go inside after waving to photographers from the steps.

Indoors, the pair made small talk about the speed with which a British government can change leaders compared to a White House transition, which takes several months.

"I am amazed it happens so fast. How do you have time to pack everything?" Kerry asked, before reporters were ushered out to allow them to speak privately.

Later, Kerry was due to meet Foreign Secretary Boris Johnson and hold a joint news conference.

Their talks will be followed with a meeting of EU foreign ministers to discuss the fragile cessation of hostilities in Syria, as well as the humanitarian situation and the conditions needed to resume UN-backed talks.

France's Jean-Marc Ayrault will press for the need to step up strikes against the Islamic State jihadist group, after last week's massacre in Nice that left 84 people dead, his office said.

Kerry and Johnson, who is due in Washington later this week, will also meet foreign ministers from Saudi Arabia and the United Arab Emirates late Tuesday to discuss the conflict in Yemen.

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