LONDON (Reuters) - British Prime Minister Theresa May on Wednesday backed a U.S. call for a cessation of hostilities in the Yemen war, a conflict that has killed at least 10,000 people and brought on the world’s worst humanitarian crisis.

Britain's Prime Minister Theresa May sits in the audience at the start of the Conservative Party Conference in Birmingham, Britain September 30, 2018. REUTERS/Toby Melville

But foreign minister Jeremy Hunt told lawmakers that Britain - an ally and arms supplier to Saudi Arabia - would be careful in any response to the Saudi role in the conflict due to commercial interests and a fear of “unintended consequences”.

May, who is under pressure to end British arms sales to Saudi Arabia to stop their use in the war, said she supported U.S. Secretary of State Mike Pompeo’s appeal for a ceasefire but a political agreement was needed.

“We certainly back the U.S.’s call for de-escalation in Yemen,” May told parliament. “A nationwide ceasefire will only have an effect on the ground if it is underpinned by a political deal between the conflict parties.”

Yemen, one of the poorest Arab countries, is locked in a nearly four-year-old war that pits Iran-aligned Houthi rebels against the government backed by Saudi Arabia, the United Arab Emirates and the West.

Its plight and the Saudi Arabia intervention have taken center stage after the killing of Saudi journalist Jamal Khashoggi at its embassy in Turkey.

The Saudi-led coalition has conducted frequent air strikes targeting the Houthis and has often hit civilians, although it denies doing so intentionally.

Foreign minister Hunt welcomed the U.S. announcement but he added that Britain’s position had to be considered for two reasons.

“Firstly we do have a commercial relationship (with Saudi Arabia). There are jobs in the UK...at stake so when it comes to the issue of arms sales we have our procedures,” Hunt said.

Second, he said, “we just have to be very careful about any action we take that there aren’t unintended consequences”.

British exports to Saudi Arabia have provided billions of pounds of revenue for the British arms trade, but opposition has grown as the conflict and humanitarian crisis in Yemen worsened.

A spokesman for Britain’s main opposition Labour Party, which backs an immediate halt to arms supplies to Saudi Arabia, told reporters it was “quite clear that the prime minister is not supporting the call for an urgent ceasefire”.

“That goes to highlight the role that the British government has played in supporting the Saudi-led bombing campaign in Yemen and the direct advice to Saudi military in that campaign by British forces under government direction.”