The Foreign Secretary is set to meet her US counterpart after Britain's controversial Chagos Islands deal was thrown into fresh crisis by Donald Trump.
Yvette Cooper will hold talks with Marco Rubio in Washington on Friday and the British Indian Ocean territory is likely to be high on the agenda.
The UK's agreement to hand sovereignty of the territory to Mauritius and lease back the largest island, Diego Garcia, which houses an important joint UK-US military base, has been repeatedly criticised by the US president after he initially appeared to support the deal.
Earlier this week, Mr Trump urged Sir Keir Starmer not to "give away Diego Garcia" despite Washington signalling its official backing for the deal on Tuesday.
Mr Trump's latest U-turn on his previous support for the agreement is reportedly because of Britain's refusal to give the White House the green light to use the base or RAF Fairford in Gloucestershire for a potential military campaign against Iran.
The Government's position is said to be due to concerns over a breach of international law, which does not distinguish between a nation carrying out an attack and one that provides support with "knowledge of the circumstances of the internationally wrongful act".
The bases can only be used for military operations with prior consent from the Government and would need to comply with UK law and the country's interpretation of relevant international law.
It comes as a judge has issued an order to temporarily block the deportation of four Chagossians who travelled to the islands to protest against the agreement to hand over sovereignty.
The men arrived on a remote part of the archipelago on Monday after sailing from Sri Lanka and say they aim to set up a permanent settlement on their "homeland".
Britain served the Chagossians with an eviction notice and threatened them with fines or prison if they did not leave.
But the men’s lawyers have successfully applied for an injunction to prevent their removal for at least seven days.
The US president is weighing fresh military action against Iran, with a second American warship moving into the region and warnings that he could go ahead if no deal on its nuclear programme is reached.
In a post on his Truth Social platform, Mr Trump said that "it may be necessary" for the US to use Diego Garcia "and the airfield located in Fairford" in order to "eradicate a potential attack by a highly unstable and dangerous regime".
A Government spokesperson refused to comment on "operational matters" and said there was a political process "ongoing between the US and Iran, which the UK supports".
"Iran must never be able to develop a nuclear weapon, and our priority is security in the region," they said.
Foreign Secretary Ms Cooper and US secretary of state Mr Rubio are expected to hold talks on UK-US cooperation on a range of areas including defence, security and trade.
The minister will also attend the National Governors' Association Reception, where she will meet with a range of US governors and discuss business opportunities for British firms as well as celebrating the 250th anniversary of American independence.
