By Louis Charbonneau and Anthony Deutsch
UNITED NATIONS/AMSTERDAM (Reuters) - U.N. chemical weapons investigators will not explicitly pin the blame on anyone in their upcoming report on the August 21 poison gas attack in Syria, but diplomats say their factual reporting alone could suggest which side in the country's civil war was responsible.
The report could easily become a bargaining chip in talks between Moscow and Western powers on conditions for Syria to give up its chemical weapons and the terms of a United Nations Security Council resolution on the matter.
Two Western diplomats said they strongly expected chief U.N. investigator Ake Sellstrom's report would confirm the U.S. view that sarin gas was used in the attack on suburbs of Damascus that killed hundreds.
One diplomat said there was a good chance the report would come out on Monday, while others predicted it could come any time from this coming weekend to next week.
While Sellstrom's report will not explicitly assign blame, Western diplomats said U.N. Secretary-General Ban Ki-moon, who has been highly critical of Syrian President Bashar al-Assad's government during the 2-1/2 year war, may choose to say whether or not he feels the facts suggest Assad's forces were responsible.
"We expect it (the report) will have a narrative of evidence," said one U.N. official. A third Western diplomat said the report will not directly accuse anyone of carrying out the attack, but it may include facts that suggest blame.
Two Western diplomats following the issue said they expected those facts would indirectly point in the direction of the Syrian government. They declined to elaborate.
Foreign Policy's blog "The Cable" cited diplomats on Thursday voicing similar views - that the facts in Sellstrom's report would suggest the Assad government's culpability.
Such facts could include the trajectories of the projectiles loaded with gas, indicating whether they came from government or rebel-held areas. It could also involve looking at the areas that were attacked, the types of weapons used, the quality and concentration of any chemical toxin traces and other facts.
"While Sellstrom may not say who's to blame, there's nothing stopping the secretary-general from interpreting the facts and saying that blame appears to point in a certain direction," the third diplomat said.
The United Nations has repeatedly declined to comment on the expected contents of the report. Syria's U.N. Ambassador Bashar Ja'afari did not respond immediately to a request for comment.
U.S. THREATENS MILITARY ACTION
Washington says forces loyal to Assad launched the attack, suburbs, which U.S. officials say used the deadly nerve agent sarin and killed over 1,400 people, many of them children.
Russian President Vladimir Putin, in an opinion piece in the New York Times, confirmed Moscow's view that there was "every reason to believe" the poison gas was used by rebels. That is the Syrian government's position as well.
The attack may have been the worst use of nerve agents since the Iran-Iraq war from 1980 to 1988 when thousands of Kurds were killed by chemical weapons, most notably in the town of Halabja.
The United States has threatened to launch military strikes against Syria to deter the government from launching further chemical attacks. But President Barack Obama's administration has said it would allow discussions on a Russian plan to place Syrian chemical weapons under international control to play out before asking the U.S. Congress to vote on authorizing the use of force.
Chemical weapons experts say U.N. investigators should stay out of the blame business.
"They are not going to say: This was a rocket used by the Syrian forces," said Dieter Rothbacher, a chemical weapons expert who trained members of the U.N. team while working at the Organization for the Prohibition of Chemical Weapons.
"As an OPCW inspector you are never supposed to pass judgment. That is up to somebody else. That's up to the guys who take the report and interpret it," said Rothbacher, who helped destroy Saddam Hussein's chemical weapons and co-owns Hotzone Solutions Group, a training and consultancy company.
Western intelligence agencies, including in the United States and Britain, say the evidence already stacks up against Assad, while experts say the rebels do not have the military capabilities to launch a widespread gas attack.
Samples collected by U.N. inspectors were split, resealed and sent to four other partner laboratories, including one in Finland and one in Sweden, U.N. officials say. The process of analyzing them takes weeks because the biomedical samples, including urine, blood and hair, need time to grow cultures.
(Editing by Peter Henderson and Christopher Wilson)