Michael Luhan, a spokesman for the group, said Syrian officials have promised more details in the next couple of days, CNN reported. OPCW, headquartered in The Hague, Netherlands, is the international watchdog for chemical weapons.
Syria was given a week's deadline under the Geneva framework for full disclosure last Saturday. Luhan described the procedure as "irregular," since the normal time limit is 60 days.
The OPCW postponed a meeting scheduled for Sunday to next week, Luhan said, because more time is needed for preparation.
U.S. Secretary of State John Kerry, at a news conference with Frans Timmermans, the Netherlands foreign minister, said he had discussed the chemical weapons issue in a long conversation with his Russian counterpart, Sergei Lavrov. He said Lavrov agreed with the need for a "firm and strong" United Nations resolution on Syria.
Syria's deputy prime minister for economic affairs, in an interview with The Guardian, said President Bashar Assad wants a cease-fire with rebels.
Qadri Jamil said Assad said he believes the 30-month civil war has reached a stalemate.
"Neither the armed opposition nor the regime is capable of defeating the other side," Jamil told the Guardian. "This zero balance of forces will not change for a while."
The Assad regime intends to call for a cease-fire at a long-delayed Geneva, Switzerland, peace conference being worked out between the United States and Russia, Jamil told the newspaper.
Other regime proposals at the conference would include "an end to external intervention ... and the launching of a peaceful political process in a way that the Syrian people can enjoy self-determination without outside intervention and in a democratic way," Jamil said.
He said the Syrian economy suffered catastrophic losses of about $100 billion in the war.
Washington and various opposition groups had no immediate response to the report.
The cease-fire, if accepted by the armed opposition, would be kept "under international observation," such as U.N. peacekeepers, provided they came from neutral or friendly countries, he said.
Syrian opposition leaders have repeatedly refused to participate in a "Geneva 2" conference unless Assad first resigns.
A June 2012 Geneva conference lasted one day and included no Syrians.
The United States and Russia have had differences over the purpose and structure of the Geneva 2 conference ever since plans for it were announced in May.
During the initial discussions, Moscow said Iran, an Assad ally, must be included. Washington said it opposed including Iran, proposing instead a "London 11" coalition of Western and Arab nations that supports the Syrian opposition.
The United States expressed its position before Hassan Rouhani was elected as Iran's president. Rouhani, who won election in June and took office in August, has been making overtures indicating a willingness to improve relations with the West and to facilitate a dialogue between the Assad regime and the opposition.
Moscow also suggested multiple delegations from the Syrian opposition attend -- the widely recognized Syrian National Coalition; the National Coordination Committee for Democratic Change, seen by much of the opposition as an arm of the regime; and a delegation of Kurds.
Fearing that would dilute the opposition's influence, the United States has insisted the SNC participate as a unified Syrian opposition delegation.
"We're fed up with this monopolistic view," Jamil told the newspaper.
Jamil also said, concerning Syria, the U.N. report on the Aug. 21 chemical weapons attack that killed more than 1,000 people was "not thoroughly objective."
He said Russia had evidence showing the rockets identified by U.N. inspectors as carrying sarin were indeed Soviet-made but came from Libya after the fall of leader Moammar Gadhafi in August 2011.
"They were loaded with chemicals by Gadhafi and exported to fundamentalists in Syria after Gadhafi fell," he said.