Saudi Arabia fueled doubts on Tuesday about whether it backs new UN sanctions to end the Iran nuclear crisis, as US Secretary of State Hillary Clinton prepared to return home.

Clinton defended the US-led push for tougher sanctions when she again charged that "evidence doesn't support" Iran's assertion that it is pursuing a peaceful atomic programme.

US officials travelling with Clinton on the mission to drum up support for tougher action against Iran expressed satisfaction and said they were "very pleased" following her lengthy talks with King Abdullah on Monday.

But Saudi Foreign Minister Prince Saud al-Faisal raised some doubt about Riyadh's support for further sanctions against Tehran when he termed the measures as a "long-term solution."

"We see the issue in the shorter term because we are closer to the threat ... We need an immediate resolution," Saud told journalists said after meeting Clinton.

It was not immediately clear whether Saud was calling for a tough and immediate UN Security Council resolution or another solution to the perceived threat from Iran.

On Tuesday, a Saudi foreign policy official stressed that Riyadh was not advocating military action but rather a linkage with the Middle East peace process as a faster and more effective means to ease regional tensions.

"There is no point in our spending all our time on sanctions which will not have an effect in the short term. We need something more tangible," he said, asking not to be identified.

"We don't want a military strike ... A military strike, we still believe, will be very counter-productive.

"We need to do something on Israel and the Palestinians ... For instance, the US could get Israel to halt (Jewish) settlements" on the occupied West Bank.

"There is a credibility issue with the US administration on promises it cannot fulfill," he said, referring to the stalled peace process.

Clinton's tour of Qatar and Saudi Arabia aimed to isolate Iran from its Arab neighbours and to put pressure on China to drop its resistance to UN sanctions targeting mainly Iran's Revolutionary Guards.

Last week, Iran began enriching uranium to 20 percent purity, which Washington and other capitals say adds to evidence it is seeking a nuclear weapon.

Tehran denies the charge, insisting its goal is peaceful nuclear energy and research.

Prince Saud played down suggestions that the oil-rich kingdom could prod Beijing not to block sanctions against Tehran by guaranteeing Beijing stable oil supplies in the event of disruption from Iran.

However, he said China, which invests heavily in and imports much of its oil from Iran, "carries its responsibilities" within the Security Council where it holds a veto power.

"And they need no suggestion from Saudi Arabia to do what they ought to do," Prince Saud added.

At the Monday night press conference, the Saudi chief diplomat also appeared to endorse Clinton's charge, which she made earlier the same day, that Iran was turning into a "military dictatorship."

The Revolutionary Guards were "supplanting" the clerical and political leadership in Tehran with a more radical line, she said.

Saud said he was inclined to believe her warnings on the Revolutionary Guards.

Iranian Foreign Minister Manouchehr Mottaki hit back on Tuesday, saying Clinton had tried but failed to dupe Gulf Arab states about a threat from the Islamic republic.

Clinton was in the Saudi Red Sea city of Jeddah on Tuesday on the last part of her three-day tour, also aimed at gaining support for Washington's push for a resumption of peace negotiations between Israel and the Palestinians.

In Jeddah, she met with the head of the Organisation of the Islamic Conference, the world's largest pan-Islamic grouping, introducing the new US envoy to the group.

She also held a "town hall" meeting at the elite private women's college Dar al-Hekma, where she was hailed as the world's "most popular woman."

Clinton told students that "evidence doesn't support" Iran's claim it has peaceful nuclear aims, and warned them if Iran is allowed to pursue its programme unchecked, it could set off a nuclear arms race in the region.

She said that if Iran gets a nuclear weapon "then other countries which feel threatened by Iran will say to themselves 'if Iran has a nuclear weapon, I'd better get one too in order to protect my people.' Then you have a nuclear arms race in the region. Then you all kinds of opportunities for problems that could be quite dangerous."