DOHA: Secretary of State Hillary Clinton takes the US drive to halt Iran's sensitive nuclear work to Saudi Arabia on Monday as she sounded more upbeat that China may eventually support sanctions against Tehran.

During a visit to Qatar on Sunday, Clinton told Iran's neighbours it appeared increasingly evident Tehran is seeking nuclear weapons and warned the Revolutionary Guards' rising power poses "a direct threat" to all.

A Clinton aide told AFP and another reporter on condition of anonymity that the US chief diplomat's remarks on China and Iran's alleged atomic weapons drive were more forceful than her previous ones.

Frustrated that a year-long drive to engage Iran in nuclear and other talks has yielded little, President Barack Obama's administration last week imposed fresh unilateral sanctions against the Islamic Revolutionary Guard Corps.

US officials also want the UN Security Council to draft new sanctions against a force they say runs Iran's nuclear programme, supports anti-US and anti-Israeli militants and cracks down on Iranian anti-government protesters.

"It's time for Iran to be held to account for its activities which do already and can continue to have destabilising effects," Clinton said in a speech to the US-Islamic World Forum, set up after the September 11, 2001 attacks.

During a three-day tour that began in Qatar, the chief US diplomat added to the US sense of urgency after Iran began Tuesday to enrich uranium to 20 percent purity while insisting its intent was peaceful.

"Iran leaves the international community little choice but to impose greater costs for its provocative steps," she said after talks with Qatar's emir Sheikh Hamad bin Khalifa Al-Thani and Sheikh Hamad bin Jassim Al-Thani, who is both foreign minister and prime minister.

"We are now working actively with our regional and international partners... to prepare and implement new measures to convince Iran to change its course," she said.

Clinton also met in Doha with Turkish Prime Minister Recep Tayyip Erdogan whose country has good ties with Iran and has repeatedly offered to serve as mediator on the nuclear issue.

A Clinton aide who asked not to be named said Turkey's stand was close to that of China, but made no comment.

Turkey's foreign minister is due to visit Iran on Monday, the aide said.

Clinton struck an upbeat note about support for sanctions among the five veto-wielding members of the Security Council -- the United States, Russia, China, Britain and France.

She said Russia has said "publicly and privately that it can and will support sanctions," and detected a shift in the Chinese position.

"The weight is maybe beginning to move toward not wanting to be either isolated or inadvertently contributing to instability that would undermine their economic interests," she said.

She recalled China's investment stake in Iran and its oil imports from that country.

On the flight to to Doha, the US assistant secretary of state for near east affairs, Jeffrey Feltman, said Washington would ask for oil-rich Saudi Arabia's help in pressing China to join the US drive for sanctions against Iran.

But Feltman neither confirmed nor denied suggestions from reporters that the administration would ask the Saudis to offer China oil supply guarantees in return for winning Beijing's support for new UN sanctions.

Clinton is due to meet Saudi Arabia's King Abdullah and Prince Saud al-Faisal, the foreign minister, in Riyadh on Monday, following a broadcast question-and-answer session with Arab and Muslim university students in Doha.

The Clinton aide said the Obama administration was open to what he called a Qatari proposal for direct US-Iran talks to break the nuclear impasse.

In her speech -- a follow-up to one that Obama gave in Egypt last October in which he called for a "new beginning" with the world's Muslims -- Clinton said she was "disappointed" the Arab-Israeli peace process remained deadlocked.

"But we need to remember that neither the United States nor any country can force a solution. The parties must resolve their differences through negotiations," she added.

"We are committed to our role in ensuring that negotiations begin and succeed," she said.

The Arab and Muslim enthusiasm that greeted Obama's victory in the US election in 2008 has given way to frustration and disenchantment, particularly over the deadlock in the peace process.

The Clinton aide said Qatar's leaders asked Clinton to press Israel to allow construction material to enter the Gaza Strip to rebuild homes destroyed in Israel's military offensive in December 2008 and January 2009.

The aide also said Clinton asked the Qataris to reopen the Israeli trade office they closed after that offensive, adding the Qataris are considering the move.