(Reuters) -

The United States and China are in strong agreement on the need for the 15-member U.N. Security Council to quickly adopt a mandatory and binding resolution on eradicating Syria's chemical weapons arsenal, a senior U.S. official said on Thursday.

U.S. Secretary of State John Kerry met Chinese Foreign Minister Wang Yi for about an hour on the sidelines of the annual gathering of world leaders at the United Nations.

"On Syria, both ministers were in strong agreement on the need for a mandatory and binding U.N. Security Council resolution," said the U.S. official, speaking on the condition of anonymity, after the meeting.

"They discussed the value of unity among the P5 (five permanent members of the Security Council) and both felt it is important for the council to act quickly and for OPCW (Organisation for the Prohibition of Chemical Weapons) to similarly act quickly," the official said.

Envoys from the United States, Russia, France, China and Britain have come to an agreement on the core of a U.N. Security Council resolution to get rid of Syria's chemical weapons, three Western diplomats said on Wednesday, but Russia denied such an accord had been reached and insisted work was "still going on."

Diplomats from the permanent Security Council members have been haggling over the details of a resolution to back an accord hammered out by Russia and the United States on September 14 in Geneva to eliminate Syrian President Bashar al-Assad's chemical weapons arsenal.

A major sticking point between Russia and Western powers has been whether the resolution is under Chapter 7 of the U.N. charter, which covers the council's authority to enforce its decisions with measures such as sanctions or military force.

Russia, a staunch ally of Assad, has made clear it would not accept an initial resolution under Chapter 7 and that any punitive measures would come only in the event of clearly proven Syrian non-compliance on the basis of a second council resolution under Chapter 7.

China has backed Russia to veto three council resolutions since October 2011 that would have condemned Syrian President Bashar al-Assad's government and threatened it with sanctions.

Assad agreed to destroy Syria's chemical weapons in the wake of a sarin gas strike on civilians in the suburbs of Damascus last month - the world's deadliest chemical arms attack in 25 years.

Washington has blamed Assad's forces for the attack, which it said killed more than 1,400 people, and President Barack Obama threatened a U.S. military strike in response. Russia and Assad have blamed the attack on rebels battling to overthrow him in a civil war that has been raging since 2011.

(Reporting by Arshad Mohammed; writing by Michelle Nichols; Editing by Will Dunham)