UNITED NATIONS- The United States is reviewing with skepticism the Syrian government's chemical arms declaration, the US envoy to the United Nations said on Tuesday as another official cautioned that intelligence suggested Syria may try to hide some weapons.

Under a Russian-US proposal, Syria agreed in September to destroy its chemical weapons program by mid-2014, averting a threat of missile strikes by Washington following an Aug 21 sarin gas attack in Damascus that killed hundreds of people.

Syria's submitted the lengthy declaration of its chemical weapons program on Oct 27 and must agree a plan with the Organisation for the Prohibition of Chemical Weapons (OPCW) by mid-November that explains in detail how and where to destroy the poisons, including mustard gas, sarin and possibly VX.

"We are still reviewing that document. We obviously bring skepticism born of years of dealing with this regime, years of obfuscation in other contexts, and of course a lot of broken promises in the context of this current war," US Ambassador to the United Nations Samantha Power said.

She noted that Syrian President Bashar al-Assad's government had so far cooperated with the joint OPCW/UN mission, which has inspected 21 out of 23 chemical weapons sites in Syria. The remaining two sites were too dangerous to reach for inspection.

Syria declared 30 production, filling and storage facilities, eight mobile filling units and three chemical weapons-related facilities. They contained about 1,000 tonnes of chemical weapons, mostly in the form of raw precursors, 290 tonnes of loaded munitions and 1,230 unfilled munitions.

"You will certainly hear from us in the event that we detect non-compliance or we detect significant discrepancies in their declaration," Power told reporters after the UN Security Council was briefed on the joint OPCW/UN mission to destroy Syria's chemical weapons program.

A second US official, speaking separately to Reuters on condition of anonymity, said, intelligence provided "indications the Syrians may be intending to hold some of their stockpile in reserve."

The official said it was important that the international community keep the Syrian government's "feet to the fire" to ensure that all Syrian chemical weapons are destroyed.

"This development is not surprising. ... At this point, it's not derailing the diplomatic process," the official said.

The CIA and the Pentagon declined comment.

More than 100,000 people have been killed and some 2.2 million people have fled during Syria's 2-1/2-year civil war. The United Nations says around 9.3 million people or about 40 percent of the population need help within the country.

The United States and Russia failed on Tuesday to agree on a date or the participants of a peace conference to end the war in Syria, said UN envoy Lakhdar Brahimi. Earlier, Damascus reiterated that Assad will stay in power regardless of a peace deal.

"The chemical weapons agreement and implementation have not changed the US position on Assad. A man who gasses his people - and who uses Scuds and all other forms of terror against his people - is not fit to govern those people," Power said.

"Eliminating Syria's chemical weapons is not a substitute for ending the violence engulfing the country," she said.