(CNN) -- U.N. weapons inspectors are expected to report their findings regarding a chemical attack in Syria early next week, sources said Wednesday, but a leading human rights group is already pointing its finger at government troops.
The inspectors collected evidence from the site of the August 21 attack outside Damascus, and laboratories have been processing the material for more than a week. A diplomatic source told CNN that the findings would be presented on Monday, while another source said the report would "likely" be presented Monday or Tuesday.
Earlier Wednesday, U.N. spokesman Farhan Haq told reporters that there was no timeline for the inspectors' report.
"They are going about their work now," Haq said. "Once they are done, they will present it to the secretary-general."
In addition, the report could be delayed amid diplomatic efforts to forestall threatened U.S. military action against Syria. U.S. Secretary of State John Kerry is headed for a two-day meeting with Russian Foreign Minister Sergey Lavrov in Switzerland over Moscow's plan to put the Syrian chemical weapons arsenal under international control.
Washington accuses Syrian government troops of using the nerve gas sarin in a large-scale attack in the suburbs of Damascus, killing more than 1,400 people -- including hundreds of children. President Barack Obama told Americans on Tuesday night that he would put off punitive strikes on Syria to pursue the diplomatic opening from Russia.
Syria's government has denied using chemical weapons, arguing its troops came under chemical attack by rebel fighters.
The U.N. team that investigated the attack is tasked with confirming whether chemical weapons were used, but its mandate doesn't include assigning blame for the attack. But the American position got some support this week from Human Rights Watch, which concluded that government forces "were almost certainly responsible" and suggested U.N. inspectors saw some of the same evidence it did.
The U.S.-based human rights group said its experts reviewed video and photos from the scene, including pictures from one source who photographed and measured remnants of rockets left at the scene. The weapons included Soviet-era 140mm rockets and an apparently Syrian-built projectile capable of holding up to 60 liters (16 gallons) of chemical agents, a Tuesday report from the group noted.
Human Rights Watch used video uploaded to the Internet and photos provided by Syrian activists as part of their review. Some of those photos included detailed measurements of a 330mm rocket so far seen only in the hands of government forces -- a model "compatible, and perhaps specifically designed, for the delivery of chemical agents."
"U.N. inspectors were also videotaped inspecting some of the same rocket remnants during their on-site visit, further confirming that the rockets are located at the scene of the attacks," the report notes.
CNN's Nick Paton Walsh and Omar Jimenez contributed to this report.