RIYADH  - US Secretary of State Hillary Clinton met King Abdullah on Friday in the Saudi capital, state news agency SPA said, as she kicked off a two-country tour aimed at raising pressure on the Syrian regime.

It said Defence Minister Salman bin Abdul Aziz, Foreign Minister Saudi al-Faisal and the kingdom's intelligence chief, Mogran bin Abdul Aziz, also took part in the meeting but gave no further details.

Clinton is due on Saturday to hold talks in Riyadh with ministers of Saudi Arabia's five Gulf Arab neighbours - Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates - before broader meetings on Sunday with Arab, Turkish and Western officials in Istanbul.

The Friends of Syria meeting in Turkey follows the inaugural one Clinton attended in Tunis at the end of February - a response to Western and Arab failure to win Russian and Chinese backing at the UN Security Council.

Aides said Clinton will discuss how to make President Bashar al-Assad comply with a new plan to end his crackdown on a pro-democracy movement, study further sanctions against his regime and consider ways to aid the opposition who will be in Istanbul.

Saudi Arabia and its neighbour Qatar have called for arming the opposition in Syria, which includes the Free Syrian Army, made up of military defectors. But an Arab League summit in Baghdad on Thursday rejected the option of arming any sides, and called on all parties to engage in a "serious national dialogue."

On Saturday, Clinton is to attend a first ministerial meeting of the Gulf Cooperation Council-US strategic cooperation forum, which is likely to also raise the perceived threat from Iran across the Gulf. "We have missile defence cooperation with some of these countries. Can we make it more efficient in a regional context, et cetera?" State Department spokeswoman Victoria Nuland said in Washington earlier in the week.

"So these are the kinds of things that we'll be talking about," she said without explicitly linking missile defence to fears over Iran.

She said the GCC talks were "primarily about peace and security in the neighbourhood. It is about helping all those countries work more closely to combat the threats that they share, the threats we work on with each of them."