United Nations Secretary General Ban Ki-moon said Friday that a report compiled by inspectors who visited Syria last month would likely show that chemical weapons were used in the Aug. 21 attack near Damascus.
Speaking in New York, Ban said the report would be released "as soon as possible."
Reuters quoted him saying, "I believe that the report will be an overwhelming, overwhelming report that chemical weapons (were) used, even though I cannot publicly say at this time before I receive this report."
The UN chief also said Syrian President Bashar al-Assad had "committed many crimes against humanity."
French Foreign Minister Laurent Fabius said the UN report would "probably" be published Monday.
"It will say that there was a chemical massacre... There will certainly be indications" of who was behind the attack, Fabius told French radio.
Kerry and Lavrov try to find 'common ground'
US Secretary of State John Kerry met with Russian Foreign Minister Sergei Lavrov Friday for a second day of talks on Syria's chemical weapons.
The talks in Geneva, which included United Nations and Arab League envoy Lakhdar Brahimi, were "constructive," according to Kerry.
Brahimi said the two diplomats' negotiation was "extremely important in itself, and for itself, but it is also extremely important for us who are working with you on trying to bring together the Geneva conference successfully."
Kerry said there were further plans to meet on the sidelines of the UN General Assembly later in September, adding that the US and Russia were "deeply committed" to a diplomatic solution, and that he and Lavrov were working hard to find "common ground."
Also in Geneva for negotiations were US and Russian chemical weapons experts trying to figure out the technical aspects of how Syrian President Bashar al-Assad could hand over his regime's stocks of chemical weapons.
Deal must be 'verifiable and enforceable'
On Friday, US President Barack Obama said he hoped for success on the so-called Russian proposal, but said he would insist that it be "verifiable and enforceable."
Senior officials of the Obama administration said the United States does not expect any UN Security Council resolution to include military force as a consequence if Syria refused to give up its chemical weapons. Increased sanctions, however, could be among the range of consequences, they said.
Syria's UN envoy said Thursday that his country had, "legally speaking," become party to the chemical weapons convention, the first step in the Russian proposal for Syria to surrender its chemical weapons to international control.
More from GlobalPost: Putin op-ed: Russia's case against striking Syria
Russian President Vladimir Putin called the decision "an important step towards the resolution of the Syrian crisis," saying it showed Assad's "serious intention" toward surrendering chemical arms.
Reports that Assad is moving his chemical weapons
However, Middle Eastern and US officials claimed that a secret Syrian military unit has been scattering the Assad regime's stockpile of poison gas to as many as 50 sites, according to the Wall Street Journal.
The officials, speaking anonymously, told the Journal that the actions of "elite Unit 450" would complicate any planned US military strike. They also said US and Israeli intelligence agencies were less confident than six months ago about the location of Assad's chemical weapons stores, which would make any verification of the weapons' destruction much harder.
Gen. Salim Idriss told CNN the same news, saying, "Today, we have information that the regime began to move chemical materials and chemical weapons to Lebanon and to Iraq."
Israeli officials told CNN they didn't believe Assad was moving weapons so soon, and Iraq denied that any Syrian chemical weapons had crossed its border.
More from GlobalPost: Kerry, Lavrov hopeful but words are 'simply not enough' on Syrian chemical weapons