Syria handed over some details of its chemical weapons program to an international watchdog on September 20.
However, the Organization for the Prohibition of Chemical Weapons, or OPCW, said it expected Damascus to provide more documentation, although it did not specify what.
The OPCW is due to meet early next week to review Syria's inventory and to agree on implementing last week's U.S.-Russian deal to eliminate the entire arsenal in nine months.
The timetable was laid down by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov a week ago in Geneva to rid Bashar Assad of chemical weapons.
That plan set a rough deadline of September 21 for Syria to give a full account of the weapons it possesses.
Security experts say it has about 1,000 tons of mustard gas, VX and sarin - the nerve agent UN inspectors found after hundreds were killed by poison following missile strikes on rebel-held areas on August 21.
Kerry said he had spoken to Lavrov by telephone on Saturday and agreed to continue cooperating.
"I might just mention that this morning I had a fairly long conversation with Foreign Minister Lavrov. We talked about the cooperation which, we both agreed to continue to provide, moving not only towards the adoption of the [Organization for the Prevention of Chemical Weapons] rules and regulations, but also, a resolution that is firm and strong within the United Nations," Kerry said.
On September 19, Kerry said a report by UN chemical weapons inspectors left no doubt that Assad forces were to blame for the August 21 attack. Kerry also called for the UN Security Council to pass a resolution including the threat of force should Assad fail to abide by the Russian-U.S. deal to dispose of his chemical weapons.
The Syrian government has accepted the plan and has already sought to join the OPCW.
Meanwhile. the party of Syria's deputy prime minister has denied reports he offered a cease-fire with the rebels if a peace conference could be convened.
Qadri Jamil had been reported as making the offer in an interview with "The Guardian" newspaper, published on September 19.
The People's Will Party led by Jamil, however, said his remarks had been "abridged and distorted" and accused "The Guardian" interviewer of being "neither precise nor professional."
Based on AP and Reuters reporting