BEIRUT — Syria’s main Western-backed opposition group on Wednesday rejected Russian accusations that rebels made sarin nerve gas and used it in a deadly chemical attack outside Aleppo in March.
The Syrian National Coalition called the charges ‘‘desperate’’ and ‘‘fabricated.’’ Russia is a key ally of President Bashar Assad’s regime.
Use of chemical weapons is an explosive issue, potentially guiding whether the West increases its aid to rebel forces. President Obama called chemical weapons use by the Assad government a ‘‘red line,’’ while such accusations against the rebels could reinforce Western misgivings about arming them.
Russia’s UN ambassador, Vitaly Churkin, blamed opposition fighters for the March 19 attack in the government-controlled Aleppo suburb of Khan al-Assal, which he said killed 26 people, including 16 government troops, and injured 86.
The rebels have blamed the government for the attack. The United States, Britain, and France have said they have seen no evidence the opposition has acquired or used chemical weapons.
‘‘The recent Russian analysis on the use of chemical weapons in Khan al-Assal is a desperate attempt by Russia to deceive the world and justify Assad’s crimes,’’ said a statement by the Coalition, a group made up mostly of exiled dissidents.
The Coalition invited a UN fact-finding mission to enter areas under rebel control in Syria to investigate the alleged use by the Syrian regime.
On Monday, the Syrian government also invited Ake Sellstrom, the Swedish head of the investigation, and UN disarmament chief Angela Kane to visit Damascus for talks on conducting an inquiry into the Khan al-Assal attack alone. The UN has sought wider access.
The government and UN have not yet been able to agree on the scope of an inquiry, and there has been no independent investigation.
Churkin delivered an 80-page report to Ki-moon on Tuesday. He said Syria asked its ally Russia to investigate the attack because of the impasse with the UN.
The samples taken from the impact site were analyzed at a Russian laboratory, Churkin said, and ‘‘there is every reason to believe that it was the armed opposition fighters who used the chemical weapons in Khan al-Assal.’’
British UN Ambassador Mark Lyall Grant told reporters Wednesday, ‘‘It’s nice that the Syrian regime has given access to Russian experts to collect samples of alleged chemical weapons use, but it is considerably more important that they give access to independent and credible UN investigators.’’
In Washington, White House spokesman Jay Carney replied, ‘‘We have yet to see any evidence that backs up the assertion that anybody besides the Syrian government has had the ability to use chemical weapons or has used chemical weapons.’’
The United States says it has ‘‘high confidence’’ that Assad’s forces have killed up to 150 people with sarin gas.