Russia-US wrangling over a resolution to enforce the destruction of Syrian President Bashar al-Assad's chemical weapons cast a shadow Monday over the start of the United Nations General Assembly.
Western diplomats said Moscow's refusal to support a Security Council resolution giving legal backing to Syria's disarmament had held up a plan to put the war-torn country's chemical arms under international control.
A meeting between US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on Tuesday could prove decisive for the plan they agreed earlier this month to head off a US military strike.
Kerry is also to meet Syrian opposition leaders on Tuesday.
Russia has accused the United States and its allies of using "blackmail" over the resolution and of seeking approval for military force in Syria.
With world leaders gathering to make speeches dominated by Syria at the UN General Assembly this week, the deadlock is a new blow to international efforts to halt the 30-month-old conflict.
Russia and the United States agreed the disarmament plan on September 14 after an August 21 chemical weapon attack in Damascus in which hundreds died. The United States has accused Assad's forces of carrying out the attack. But the Syrian government, backed by Russia, blames opposition rebels.
Moscow and Washington have sent a blueprint of what would be one of the biggest disarmament missions ever staged to the Organization for the Prohibition of Chemical Weapons (OPCW), diplomats said.
"The details of how to destroy the weapons are basically agreed, but everything is held up by the enforcement -- and that is between Russia and America at the Security Council," a UN diplomat told AFP.
Kerry has demanded a "strong" Security Council resolution to enforce the plan. Lavrov at first said a resolution under Chapter VII of the UN Charter would be used. But he has since rejected such a measure.
Chapter VII can allow military force or economic sanctions. But Western diplomats say a resolution now being discussed with Russia does not threaten either.
They say they want Chapter VII used so that demands to make Assad declare all chemical weapon sites and hand over the banned arms can be enforced under international law.
"Our American partners are beginning to blackmail us" by linking the disarmament plan with the Security Council resolution, Lavrov said in a Russian television interview Sunday.
"Our partners are now blinded by their ideological goal of regime change."
The five permanent Security Council members -- the United States, Russia, France, Britain and China -- held new contacts on a resolution on Monday.
French Foreign Minister Laurent Fabius reaffirmed that any resolution had to allow for possible measures under Chapter VII of the UN Charter if Assad fails to keep the plan.
He added at a news conference that the resolution had to call for those responsible for chemical attacks in Syria to "face justice."
But Fabius said he believed it was still possible to pass a UN resolution this week.
A senior US State Department official said the OPCW accord and the UN resolution had to work "hand-in-hand."
"It is in the UN Security Council that you have the ability to enforce whatever the OPCW comes up with. So the two have to speak in harmony."
The official expressed hope that the Kerry-Lavrov meeting on Tuesday would break the deadlock.
"You've seen this movie enough times to know how complex and difficult these kinds of negotiations are and sometimes they take more time than you initially thought," the US official said.
UN leader Ban Ki-moon is to call together foreign ministers from the Security Council powers on Wednesday for a lunch to discuss the Syria crisis.
He is also expected to hold talks with Kerry and Lavrov in a bid to name a date for a peace conference in Geneva. UN spokesman Martin Nesirky said the meeting would "likely" be held on Friday.