Britain's new Foreign Secretary William Hague has criticised Iran's nuclear programme ahead of his first visit to Washington on Friday, in comments to a newspaper.

Hague, who embarks on his inaugural overseas trip in his new role just three days into Britain's coalition government, told the Times that "tackling nuclear proliferation [in] Iran" was a priority for the administration.

"Iran's behaviour in recent years has been unacceptable to the great majority of the international community," he said.

Hague indicated that Britain would continue to push for United Nations sanctions, said the paper, as he prepared for talks with US Secretary of State Hillary Clinton.

The United States is in the process of enlisting support for a fourth round of sanctions against Iran at the UN Security Council, as Washington steps up efforts to halt the Islamic republic enriching uranium.

Administration officials have signalled "good progress" from not only Russia but also China, both veto-wielding council members.

Washington fears Iran is trying to develop atomic weapons, while Tehran insists its nuclear programme is peaceful.

Hague, a member of the Conservative party which this week formed a coalition government with the smaller Liberal Democrat party, listed the war in Afghanistan as another focus of the administration's foreign policy.

"Our immediate priorities are making sure that we get to grips with Afghanistan and tackling nuclear proliferation [in] Iran," he told the paper.

The foreign secretary's early trip to the US takes up a relationship that was sometimes perceived as awkward under Gordon Brown's premiership.

Obama gave Britain's new Prime Minister David Cameron strong backing after he was installed in the top job Tuesday, praising the Conservative party chief as a "smart, dedicated, effective leader."

A US official played down concerns about views on Iran expressed by the Liberal Democrats, who came third in the May 6 elections but are now in office after a power-sharing deal with the Conservatives.

The Lib Dems' manifesto states the party is opposed to military action against Iran, while Hague -- in line with the US -- has always been careful not to rule out the need for such action to stop Iran getting an atomic weapon.

State Department spokesman Philip Crowley brushed off concerns about the party's stance.

"These are things said in campaigns but now they have to put together a programme to govern," he said, in comments cited by the Times.

"This is an extraordinarily important relationship."