John Kerry: "We are both deeply concerned about the acts on all sides"
US Secretary of State John Kerry has described as "constructive" talks with his Russian counterpart Sergei Lavrov on securing Syria's chemical weapons.
The two men began a second day of talks in Geneva by meeting UN-Arab League envoy Lakhdar Brahimi to discuss the wider issue of peace in Syria.
Talks between Mr Kerry and Mr Lavrov on the weapons issue began on Thursday and could continue over the weekend.
Mr Kerry said they were working hard to find "common ground".
The BBC's Paul Adams in Geneva says this is a moment of diplomatic momentum over Syria which has not been seen for a couple of years and both parties want to make the most of that.
Russian President Vladimir Putin on Friday called Damascus's decision to join the Chemical Weapons Convention "an important step towards the resolution of the Syrian crisis" and said it showed the "serious intention" of President Assad "to follow this path".
The leaders of Syria's other key allies, China and Iran - meeting at a regional summit in Kyrgyzstan - also welcomed President Assad's move.
But Syrian rebels say it will not stop the killing. Free Syrian Army spokesperson Louay Moqdad told the BBC Mr Assad still has plenty of conventional weapons at his disposal and he is attempting to "buy time" with the help of the Russians.
Mr Kerry and Mr Lavrov met UN-Arab League envoy Lakhdar Brahimi at the UN headquarters in Geneva to discuss his attempts to keep efforts for a peace process on the table.
Speaking afterwards at a brief news conference, Mr Kerry said they planned to meet again on the sidelines of the UN General Assembly in New York later in the month to try and set a date for a long delayed peace conference, known as Geneva 2.
He said his talks with Mr Lavrov so far had been "constructive" but progress in New York would depend on "the capacity to have success here in the next hours, days, on the subject of the chemical weapons".
He said both the US and Russia were "deeply committed to a negotiated solution" to the conflict in Syria and he and Mr Lavrov were "working hard to find the common ground to be able to make that happen".
Mr Lavrov said he welcomed the chance to discuss the "longer term goal" of peace in Syria, and that now Syria has joined the Chemical Weapons Convention it is necessary "to design a road which would make sure that this issue is resolved quickly, professionally, as soon as is practical".
The US and Russia have sent large teams to Geneva that include weapons experts as well as diplomats.
If the talks 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 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, but did not immediately say if it had accepted the application.
President Assad said data on chemical weapons would start to be passed to the UN after 30 days.
But Mr Kerry has rejected this, saying such standard procedures are not relevant when chemical weapons have already been used.
Washington and its allies accuse 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 envoy to the UN, Bashar Jaafari, later said that "legally speaking", Syria is now a full member of the convention.
Russia, supported by China, has blocked three previous draft UN resolutions condemning the Assad government.
More than 100,000 people have died since the uprising against President Assad began in 2011. Millions of Syrians have been displaced.