MOSCOW -- Russia's foreign minister said Saturday that the evidence put forth by the United States of chemical weapons use in Syria apparently doesn't meet stringent criteria for reliability.

The Obama administration said this week that it will give lethal aid to Syrian rebels in light of evidence that President Bashar Assad's forces used chemical weapons in the country's civil war.

In Moscow, Foreign Minister Sergey Lavrov said the material does not include guarantees that it meets the requirements of the Organization for the Prohibition of Chemical Weapons. He said the organization specifies that samples taken from blood, urine and clothing can be considered reliable evidence only if supervised by organization experts from the time they are taken up to delivery to a laboratory.

The OPCW is the autonomous body for implementing the international Chemical Weapons Convention that went into effect in 1997. Its website says Syria is one of six countries that have not signed or acceded to the convention.

A spokesman for the organization, based in The Hague, Netherlands, could not immediately be reached for comment.

Lavrov, after meeting with his Italian counterpart Emma Bonino, scoffed at suggestions that Assad's regime would use chemical weapons now in light of its apparent growing advantage against the rebels.

"The regime doesn't have its back to the wall. What would be the sense of the regime using chemical weapons, moreover at such a small quantity?" he said.

Russia has blocked proposed U.N. sanctions against Assad's regime and acknowledged last month that it has contracted to supply advanced S-300 air-defence missiles to Syria. But President Vladimir Putin and other officials say the policies do not constitute overt support for Assad.