Russia is a key ally of President Bashar Assad's regime. In the past the UK and France have both said that they have proof the regime has used chemical weapons.
President Barack 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 on July 9 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 others. Churkin delivered an 80-page report to UN Secretary General Ban Ki-moon 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."
The rebels have blamed the government for the attack. "Evidence provided by parties that support Assad's tyrannical regime with money, weapons, and ammunition is false and clearly fabricated," said the statement by the SNC, a group made up mostly of exiled dissidents.
"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," it added. "The Syrian people consider Russia (to be) Assad's partner in the murder of innocent Syrian civilians."
The US, Britain and France have said they have seen no evidence that the opposition has acquired or used chemical weapons. All three countries have in the past year accused the Assad regime of using chemical weapons citing their own tests.
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 US says it has "high confidence" that Assad's forces have killed up to 150 people with sarin gas.
The Coalition invited the UN to enter areas under rebel control in Syria to investigate the alleged use of chemical weapons by the Syrian regime.
On Monday, the Syrian government also invited Ake Sellstrom, head of the UN fact-finding mission on allegations of chemical weapons use in Syria, and UN disarmament chief Angela Kane to visit Damascus for foreign minister level talks on conducting an inquiry into the Khan al-Assal attack alone. The UN has sought wider access.
But up to now the government and UN have not been able to agree on the scope of an inquiry, and there has been no independent investigation.
The war in Syria has so far claimed more than 93,000 lives according to the UN and clashes are continuing unabated.