By Michelle Nichols and Louis Charbonneau
NEW YORK, Sept 17 (Reuters) - Diplomats from the United States, Russia, Britain, France and China launched negotiations on Tuesday on a Western-drafted resolution that would demand the destruction of Syria's chemical arsenal in line with a U.S.-Russian deal agreed last weekend.
Nearly an hour of initial talks ended with an agreement to meet again on Wednesday, diplomats said.
Tuesday's meeting came a day after U.N. investigators confirmed the use of sarin nerve agent in an Aug. 21 poison gas attack outside the Syrian capital. The United States, Britain and France said the long-awaited U.N. report proved beyond any doubt that Syrian government forces were responsible.
Erin Pelton, spokeswoman for the U.S. mission to the United Nations, said the five permanent members of the U.N. Security Council - known as the "P5" - were discussing a joint U.S.-British-French draft but declined to comment at length.
"In order to respect the integrity of these negotiations, we will not be reading out the details of today's meeting or the draft resolution," she said.
Britain's U.N. Ambassador Mark Lyall Grant told Reuters that the five would hold further consultations soon.
"The P5 had a discussion of the text but we will be meeting again," he said after the meeting at the U.S. mission ended. "Obviously everyone has to put it back to their capitals and then we'll have a further discussion tomorrow."
Russian Ambassador Vitaly Churkin also declined to comment in detail, saying "I don't have any initial reaction" to the Western draft resolution.
"We're doing a very important thing," Churkin told Reuters. "We originated a very important proposal and we hope it's going to be implemented without any interference."
The resolution is intended to support a U.S.-Russian deal agreed in Geneva on Saturday which calls for Syria to account fully for its chemical weapons within a week and for the removal and destruction of the entire arsenal by mid-2014.
That deal was agreed after President Barack Obama threatened to launch air U.S. strikes against Syria because of the Aug. 21 poison gas attack. Syria and Russia blame the sarin attack, which killed hundreds, on Syrian rebels.
U.N. diplomats told Reuters it remained unclear when a vote on a Security Council resolution could take place.
Before any draft resolution is put to a vote in the 15-nation Security Council, diplomats said, the Organization for the Prohibition of Chemical Weapons' Executive Council in The Hague will have to approve a decision setting down special procedures for dealing with Syria's chemical weapons.
Diplomats in New York said the OPCW decision was expected on Friday at the earliest. That meant a council vote was possible over the coming weekend, they said.
Russia, backed by China, has vetoed three council resolutions since October 2011 that would have condemned the Syrian government and threatened it with sanctions.
One diplomat said the U.S.-British-French draft was similar to an initial French text Reuters reported on last week. That draft called for giving Syria an ultimatum to give up its chemical weapons or face "necessary measures."
The current Western draft, diplomats said, would still condemn and blame Syrian President Bashar al-Assad for the use of chemical weapons in Syria and refer the Syrian civil war to the International Criminal Court for possible war crimes indictments.
The draft is also written so that its provisions are under Chapter 7 of the U.N. charter, which covers the Security Council's authority to enforce its decisions with measures such as sanctions or the use of force. The measures called for in the initial French draft were also under Chapter 7.
"Broadly, the outline is still the same," a diplomat said, while noting that it now includes elements of the weekend Geneva agreement and incorporates suggestions from all three Western powers.
Russia 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 Security Council resolution under Chapter 7.