"Building a stronger relationship cannot happen overnight. It takes patience, persistence and hard work from all of us," she said.

"We are and will remain committed to the president's vision for a new beginning."

Iran sanctions

Clinton's comments at the forum, which is jointly organised by the Qatari foreign ministry and the US Brookings Institution, came only hours after she arrived in Doha for the start of a three-day visit to the region.

She is using the trip to win Arab backing for the resumption of Israeli-Palestinian peace negotiations and tougher sanctions against Iran.

The US is making efforts to enlist the UN Security Council to impose a fourth round of sanctions on Iran over its controversial nuclear programme, which Tehran says is to simply to meet its civilian needs.

"Iran leaves the international community little choice but to impose greater costs for its provocative steps," Clinton said.

"Together, we are encouraging Iran to reconsider its dangerous policy decisions."

US officials hinted that Saudi Arabia could help in that effort diplomatically by offering Beijing guarantees it would meet Chinese oil requirements, a step that might ease Beijing's reluctance to impose further sanctions on Iran.

China, which wields a veto on the Security Council, has lucrative commercial relationships with Iran and, along with Russia, has worked to dilute previous sanctions resolutions.

'Sharpen the question'

"We believe that all countries have a part to play in helping to sharpen the question for Iran," Jeffrey Feltman, the US assistant secretary of state, said.

"We would expect them [the Saudis] to use these visits, to use their relationships, in ways that can help increase the pressure that Iran would feel," he added.

Clinton is to hold talks with King Abdullah of Saudi Arabia on Monday.

Other US officials, who spoke on condition they not be identified, said they believed Saudi Arabia had made some gestures towards China on fuel assurances but gave no details.

"There have been some recent, positive moves," said one official, without elaborating.

Meanwhile, Recep Tayyip Erdogan, the Turkish prime minister, in remarks earlier on Sunday, said Turkey is willing to serve as the venue for an exchange of Iranian nuclear fuel in a potential settlement between the West and Iran.

"The International Atomic Energy Agency has said Turkey could serve as the centre for the exchange of uranium ... but there is no agreement up until now," he said.

"If Turkey is chosen, it will do what it is asked to do