Kerry, 69, who took over from Hillary Clinton earlier this month, held talks with British Prime Minister David Cameron and foreign secretary William Hague today.
Topics on the agenda included the status of the Falklands Islands, claimed by both the UK and Argentina, as well as the crisis in Syria and Iran's nuclear programme.
He will be heading off to Germany as part of a nine-country, 11-day "listening tour" covering Berlin, Paris, Rome, Ankara, Cairo, Riyadh, Abu Dhabi and Doha.
According to senior US State Department officials, Kerry's decision to make his first trip to Europe, unlike his predecessor Hillary Clinton who chose to tour countries in Asia and the Pacific, sends a strong signal to America's closest European partners.
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He is keen to map out a new era in American diplomacy after taking over from Clinton as the 68th secretary of state.
Kerry has spent almost three decades in the US Senate as a member of the powerful Foreign Relations Committee.
The former Massachusetts senator and 2004 Democratic presidential candidate arrived here late yesterday as the Obama administration tried to salvage a Syrian conference that he plans to attend this week in Rome.
Kerry has said he plans to use the trip to propose ideas on persuading the Syrian president to step aside.
The US has sought Russia's backing to convince Syrian President Bashar al-Assad that he is isolated internationally.