US Secretary of State Hillary Clinton departs on Thursday for fresh diplomacy aimed at halting Syria's bloodshed, but there is little sign the Obama administration is ready to deviate from its hands-off approach.

Hillary’s talks in Riyadh with foreign ministers from Gulf states will likely be anchored by a new peace proposal from UN-Arab League special envoy Kofi Annan. It's the latest bid to broker a diplomatic end to over a year of fighting between President Bashar al-Assad's troops and opponents to his family's decades-long rule.

Hillary is expected to use a special meeting on Syria in Istanbul on Sunday to pressure the country's divided opposition to unite. Without that step, there is little chance Assad's opponents can oust him without a military intervention the West clearly does not want.

While the Syrian leader has reportedly accepted Annan's six-point plan in principle, fighting continued in Syria on Wednesday, as government forces bombarded cities up and down the country and stormed villages, forcing thousands to flee.

The Obama administration's approach to the crisis in Syria, with its capable military and its strategic location between US allies Turkey and Israel, will continue to be "wary and slow-moving," said Michael O'Hanlon, a military expert at the Brookings Institution.

For now at least, the White House seems more concerned by worries a military intervention could draw the United States into another messy Middle East conflict than it does by calls from Republican critics such as John McCain for a more martial US stance.

"If Assad has reached a turning point and really made headway against insurgents, I believe there is a good chance he will 'win' without too much American pushback," O'Hanlon said.