(CNN) -- A team of Russian experts has found that chemical weapons were "clearly" used in Syria, Moscow's U.N. ambassador said Tuesday.
"There is every reason to believe that it was armed opposition fighters who used the chemical weapons in Khan al-Assal," Vitaly Churkin said.
The experts visited Khan al-Assal, where Syria claimed rebels had used chemical weapons in a March attack. At the time, rebels accused Syria of using chemical weapons in another part of the country.
Both sides denied the claims.
"The results of the analysis clearly indicate that the ordnance used in Khan al-Assal was not industrially manufactured and was filled with sarin," Churckin said Tuesday.
In April, U.S. Defense Secretary Chuck Hagel said the "United States has evidence that the chemical weapon sarin has been used in Syria on a small scale."
Last month, the White House accused Syria of crossing a "red line" with its use of chemical weapons against its people.
Throughout the crisis in Syria, Russia has been at odds with the United States and many other countries calling for tough action against the Syrian regime.