John Kerry has said the United States takes "no position" on whether the Falkland Islands belong to Britain or Argentina, ahead of a referendum on the disputed territory.
Speaking alongside William Hague during a press conference in London on Monday, the newly appointed secretary of state repeated a long-held US position of neutrality.
"I am not going to comment, nor is the president on a referendum, that has yet to take place and hasn't taken place.
"Our position on the Falklands has not changed. The US recognises de-facto UK administration of the islands but takes no position of the question of sovereignty claims.
"We support cooperation between UK and Argentina on practical matters, we continue to urge a peaceful resolution."
His refusal to give American support for the British claim over the islands is likely to irritate Downing Street, as well as many MPs who feel the US should back its old ally in the dispute.
Kerry held talks with David Cameron earlier on Monday, however it is understood the pair did not discuss the territorial dispute.
In March the islanders will be given a vote on whether they want to remain a British overseas territory in response to Argentina's claims over sovereignty. The islanders are expected to overwhelmingly vote in favour of the status quo.
Kerry, who visited London as part of his first overseas tour as secretary of state, was effusive in his praise for the US-UK alliance.
He said: "When you think of everything that binds the US and Great Britain - our common values, our long shared history, our ties of family and friendship, there is a reason why we call this the special relationship, or as President Obama and Prime Minister Cameron wrote, `a partnership of the heart'.
"In the 20th century our countries fought for freedom side by side and fought for survival together in war, we thrived together in peace and we stood together time and time again in order to meet the world's great challenges.
"In the 21st century, we may face a new and more complex set of challenges, but I absolutely know that we face them together just as we did in the last century.
"And together, it is absolutely clear that our partnership remains stronger than ever."
On a personal note, Kerry recalled how he visited London as a young child and got lost at the zoo, adding: "I want to thank somebody for finding me."