The US and Russian foreign ministers are due to hold their second round of talks in Geneva on how to secure Syria`s chemical weapons.
US officials said Thursday`s meeting was comprehensive and lasted about an hour. Talks could continue over the weekend.
The BBC`s Paul Adams in Geneva says it appears large disagreements still exist between the two governments.
UN-Arab League envoy Lakhdar Brahimi is due to attend Friday`s meeting.
Our correspondent says Mr Brahimi will want to know whether the talks can develop into a fresh round of negotiations over a wider political settlement.
On Thursday, Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry said they hoped the plan to put Syria`s chemical weapons under international control could avoid US military action.
Russia announced its proposal for dealing with the escalating chemical weapons crisis on Monday, as the US Congress was preparing to debate whether to back President Barack Obama`s moves towards military strikes.
The UN has confirmed it has received documents from Syria on joining the Chemical Weapons Convention, a key step in the Russian plan.
Syria`s President Bashar al-Assad said data on chemical weapons would start to be passed to the UN after 30 days.
But Mr Kerry rejected this, saying such standard procedures were not relevant when chemical weapons had already been used.
Washington accuses the Syrian government of killing hundreds of people in a chemical attack in the Ghouta area of the capital, Damascus, on 21 August. The government denies the allegation, blaming rebels.
In an interview with Russian TV, President Assad cautioned that Russia`s proposal was "not unilateral", adding: "Syria will accept it if America stops military threats and if other countries supplying the rebels with chemical weapons also abide by the agreement."
Syria`s UN envoy Bashar Jaafari later said that "legally speaking", Syria was now a full member of the convention.
`Not a game`
While UN chief Ban Ki-moon welcomed the application, the UN would not immediately confirm that it had been accepted.
On Russia`s Rossiya 24, President Assad says the US must "stop supplying terrorists with weapons"
Diplomats said it was possible that the application still had missing elements and it could be sent back to Damascus.
Before Thursday`s talks, Mr Kerry said the world was watching to see whether the Assad government would honour its commitments to give up its chemical arsenal.
"This is not a game. It has to be real, it has to be comprehensive, it has to be verifiable, it has to be credible, it has to be... implemented in a timely fashion. Finally, there ought to be consequences if it doesn`t take place," he said.
Mr Lavrov said a "solution" to the chemical weapons issue in Syria would make any military strike by the United States unnecessary.
The US and Russia have sent large teams to Geneva that include weapons experts as well as diplomats.
If the talks in Geneva are successful, the US hopes the disarmament process will be agreed in a UN Security Council resolution.
However, Russia regards as unacceptable any resolution backed by military force, or a resolution that blames the Syrian government for chemical attacks.
Moscow has already objected to a draft resolution that would be enforced by Chapter VII of the UN charter, which would in effect sanction the use of force if Syria failed in its obligations.
Russia, supported by China, has blocked three previous draft resolutions condemning the Assad government.
More than 100,000 people have died since the uprising against President Assad began in 2011.
Source: BBC
BDST: 1003 HRS, SEP 13, 2013
RS/GCP