The French government has confirmed that sarin gas has been used in Syria, though it would not confirm where it was used or by whom.
The use of chemical agents has been at the forefront of the more than two-year-old fighting in Syria between the regime of President Bashar al Assad and a coalition of opposition fighters. Both sides have claimed the other has used chemical weapons in the civil war, which Barack Obama says would be a "red line" without offering any specific consequences.
The White House remains distant from reaching a conclusion, the BBC reports, calling for more information.
A U.N. report released Tuesday says there are "reasonable grounds to believe that chemical agents have been used as weapons" in Syria, including potentially those from Assad's known stockpile.
The Office of the High Commissioner for Human Rights report says both regime forces and opposition fighters may have employed these weapons. A rebel leader said in May that the opposition has neither the ability nor the motivation to use chemical weapons.
There have been four likely attacks, the U.N. says: March 19 in Aleppo and in Damascus; April 13 in Aleppo and April 29 in Idlib.
Western countries, including France, Israel and the U.K. have all confirmed that some chemical weapons have been used within Syria. U.S. Secretary of State John Kerry said last month there was "strong evidence" that Assad had employed such weapons in the fighting that has killed tens of thousands and displaced millions from their homes.
"This fight is about the terrible choices the Assad regime has made, with its willingness to kill anywhere from 70,000 to 100,000 of its own people now, to use gas, which we believe there is strong evidence of, to massacre people with Scud missiles, with artillery, and to really try to pretend this is somehow an outside affair, when really this is people within Syria fighting for a different future," Kerry said during a Google Hangout at the State Department on May 10.
Two French journalists were reportedly injured in an attack outside Damascus last month and treated for what French doctors said was exposure to sarin.
The White House remained tight-lipped on these accounts last week.
"We're working with our partners, we're working with the opposition on this effort... and the reason that we are working so hard on this is because the use of chemical weapons does raise some serious concerns," said spokesman Josh Earnest. "We're committed to conducting a pretty rigorous investigation here because this is a serious matter."
The samples tested in France were taken from unspecified locations in Syria, according to the BBC. The results of the testing were given to the U.N.