A U.S. State Department cable indicated the Syrian military likely used chemical weapons last month in a deadly attack in Homs, The Cable magazine reported.
U.S. diplomats in Turkey investigated allegations Syrian President Bashar Assad used chemical weapons, making a "compelling case" government forces used poison gas, the magazine reported Wednesday.
The cable, signed by Scott Frederic Kilner, the U.S. consul general in Istanbul, and sent to Washington last week, outlined results of the investigation into reports from Syria chemical weapons had been used in Homs Dec. 23. An official in President Obama's administration said the investigation was one of the most thorough efforts the U.S. government undertook to scrutinize claims by Syrian sources.
Rebels and government forces have been fighting since March 2011.
An Obama administration official who reviewed the document, classified at the "secret" level, spoke about it with The Cable.
"We can't definitely say 100 percent, but Syrian contacts made a compelling case that Agent 15 was used in Homs on Dec. 23," the official said.
The regime's use of chemical weapons would cross the "red line" President Obama established in an Aug. 20 statement. So far, the administration hasn't undertaken any major policy changes in response to the classified cable, but a meeting of top administration officials was scheduled for this week.
The Cable said it was told many believe Assad is testing U.S. resolve.
"This reflects the concerns of many in the U.S. government that the regime is pursuing a policy of escalation to see what they can get away with as the regime is getting more desperate," an administration official said. "It's incidents like this that lead to a mass-casualty event."
Activist and doctors in Homs have been distributing evidence of the Dec. 23 incident in recent weeks, The Cable said. Videos of the victims, posted on YouTube and Facebook, portray victims gasping for breath and choking on vomit.
Experts said the symptoms match the effects of Agent 15, also known by the NATO code BZ, an incapacitating agent that could cause confusion or hallucinations and is listed under schedule 2 of the Chemical Weapons Convention, to which Syria is not a signatory.
The Cable said it spoke with two doctors who were in Homs Dec. 23 and treated the victims. The doctors said the chemical weapon used in the attack may not have been Agent 15, but they are certain it was a chemical weapon. The doctors attributed five deaths and about 100 cases of severe respiratory, nervous system and gastrointestinal ailments to the gas.
"It was a chemical weapon, we are sure of that, because tear gas can't cause the death of five people," Dr. Nashwan Abu Abdo, a neurologist, told The Cable.
The State Department declined to comment on the report or whether chemical weapons were used in the Homs attack, telling The Cable the administration believes Assad's chemical weapons are secure.
"As you know, the United States closely monitors Syria's proliferation-sensitive materials and facilities, and we believe Syria's chemical weapons stockpile remains secured by the Syrian government," State Department spokesman Patrick Ventrell told The Cable. "We have been clear that if Assad's regime makes the tragic mistake of using chemical weapons or failing to secure them, it will be held accountable."