Western powers are preparing a tough response if Syrian President Bashar Assad's regime deploys chemical or biological weapons in its civil war, key European officials warned 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 them, could use chemical or biological weapons if it were attacked from outside.
"Our response ... would be massive and blistering," if Assad's forces used such weapons, French Foreign Minister Laurent Fabius told RMC radio.
Britain's Foreign Secretary William Hague told the House of Commons he had asked U.N. Secretary-General Ban Ki-moon to begin preparations so the U.N. could quickly deploy experts to make checks if "we have any reports of such chemical weapons being used or moved."
Hague said the U.S., France and Britain had been clear to Assad that the use of chemical weapons could prompt a dramatic change in their handling of Syria's civil war. President Barack Obama has called the issue a "red line" for the U.S.
"We have not ruled out any options as this crisis deepens," Hague told lawmakers.
Britain's Prime Minister David Cameron has said the U.K. had no plans to intervene militarily in Syria, but that the use of chemical weapons would lead him to "revisit" that approach.
Fabius confirmed that Western countries were monitoring the movement of the weapons in Syria to be ready to "step in" immediately if necessary. "We are discussing this notably with our American and English partners," he said.
The French minister said Russia and China were "of the same position," but did not elaborate. 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.
"The Russian position on this is only likely to change when the situation on the ground changes further, to a substantial degree," said Hague, reflecting talks he and Cameron held with Russian President Vladmir Putin during the London Olympics last month.
Since March 2011, activists estimate that more than 20,000 people have been killed in Syria, where a popular uprising against the Assad regime evolved over the months into a full-blown civil war.
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 Associated Press 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."
The foreign ministries of both China and Russia declined immediate comment on Monday.
Syria's opposition has urged outside military help against Assad's armed forces.
"I am going to be very clear. We are requesting military intervention in order to protect Syrian civilians who have been constantly murdered over the last year and a half," the head of the Syrian National Council, Abdelbaset Sieda, said in Madrid on Monday.
Spain's Foreign Affairs Minister Jose Manuel Garcia Margallo, who met with Sieda, said his country would continue to press for a united EU approach to Syria and urged Syrian opposition groups to overcome their divisions and join together against the Assad regime.
The new U.N. envoy to Syria, Lakhdar Brahimi, acknowledged Monday that brokering an end to the civil war is a "very, very difficult task."
In London, Hague urged the West and its allies to accelerate planning for a post-Assad regime.
"Assad's departure from power is now inevitable. His regime is doomed, and the international community must plan rapid support to a new government in Syria now," said Hague.
Stringer reported from London. Harold Heckle in Madrid and Nataliya Vasilyeva in Moscow contributed to this report.