The White House said on Saturday it was consulting with international partners on 'next steps' in the Syrian crisis after UN observers suspended operations there in response to violence that has escalated despite a ceasefire deal.

'We call again on the Syrian regime to uphold its commitments under the Annan plan, including the full implementation of a ceasefire,' White House spokesman Tommy Vietor said in a statement.

US officials have voiced growing skepticism about Syrian President Bashar al-Assad's willingness to comply with the tattered plan brokered by international mediator Kofi Annan.

But Washington and its Western allies have shown no appetite for a Libya-style military intervention even as Moscow has helped shield Assad from tougher UN measures.

'At this critical juncture, we are consulting with our international partners regarding next steps toward a Syrian-led political transition as called for in Security Council resolutions,' Vietor said. But he provided no specifics.

'The sooner this transition takes place, the greater the chance of averting a lengthy and bloody sectarian civil war,' Vietor said.

Chief monitor General Robert Mood said earlier the fighting in Syria posed a threat to his unarmed observers and prevented them from carrying out their mandate to oversee Annan's widely ignored April 12 ceasefire. One of the observer mission's patrols was fired upon four days ago.

Diplomats say Mood is expected to brief the U.N. Security Council on Monday or Tuesday about the unrest in Syria.

US President Barack Obama will hold talks with Russian President Vladimir Putin on Monday on the sidelines of a G20 summit in Mexico, but expectations are low for any significant progress for breaking the deadlock on Syria.-Reuters