The GCC and the US are set to announce a new "strategic forum" on security today. It will be announced as US Secretary of State Hillary Clinton attends a first ministerial meeting of the GCC-US strategic co-operation forum in Riyadh, which will discuss the heightened threat from Iran, officials said.

Clinton yesterday met King Abdullah of Saudi Arabia to discuss regional security, the crisis in Syria and oil policy differences.

Clinton, who was starting her two-nation tour of the region, will then attend a Friends of Syria meeting in Istanbul, Turkey, tomorrow.

"We have missile defence co-operation with some of these countries. Can we make it more efficient in a regional context?" State Department spokeswoman Victoria Nuland said in Washington earlier.

"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."

At the last summit of Gulf leaders in Riyadh in December, King Abdullah said its members should join together as "a single entity", a remark widely interpreted as a demonstration of unity against Iran.

In October, the US said it had uncovered an Iranian-backed plot to assassinate the Saudi ambassador to Washington. Iran denied any involvement in the alleged conspiracy, which was interpreted in Riyadh as part of a broad campaign being waged by Tehran against Saudi.

US President Barack Obama initially sought to engage Iran after his 2008 election. But he has since pushed for stronger sanctions to halt a suspected Iranian drive to acquire nuclear weapons.