Western powers are preparing a tough response in case Syrian President Bashar Assad's regime deploys chemical or biological weapons in its civil war, France's foreign minister said Monday.

Syria's leadership has said the country, which is believed to have nerve agents as well as mustard gas and Scud missiles capable of delivering these lethal chemicals, could use chemical or biological weapons if it were attacked from outside.

President Barack Obama has called it a "red line" for the U.S. if Assad's regime were to use chemical or biological weapons, and France has been ratcheting up its language on the issue.

Speaking on RMC radio Monday, French Foreign Minister Laurent Fabius said "we are discussing this notably with our American and English partners." If Syria uses such weapons "our response ... would be massive and blistering," he said.

Fabius added that Russia and China are "of the same position," but acknowledged frustration at their continuing support for Assad.

The foreign ministries of both China and Russia declined immediate comment on Monday.

But, since the start of the Syrian conflict Beijing has been consistent in its stance that it should be settled through negotiations and not by outside forces.

Moscow is Syria's chief ally, and Russian Deputy Foreign Minister Gennady Gatilov told the AP in a recent interview that Russia has the Syrian government's assurances that chemical weapons will not be used. Gatilov said Russia will "work toward the goal of preventing such things from happening."

China and Russia have repeatedly used their veto powers in the U.N. Security Council to block U.S.- and Arab-backed action that could have led to sanctions against Assad's regime.