The Syrian government and rebels accused each other of using such weapons in a rocket attack near Aleppo on Tuesday that killed 26 people.
 

However, a U.S. official has said it increasingly appeared that a chemical weapon was not used. Nor has any previous such deployment been confirmed.
 

But in a letter to EU foreign policy chief Catherine Ashton, sent before a meeting of EU foreign ministers in Dublin to discuss Syria, ministers Laurent Fabius and William Hague said: "The crisis is increasingly threatening regional stability... and we are increasingly concerned about the regime's willingness to use chemical weapons."
 

In the letter, a copy of which was seen by Reuters, Fabius and Hague reiterated calls for the European Union to ease its arms embargo on Syria to allow for more help to the opposition. The issue will be discussed in Dublin on Friday.
 

The two ministers also said it would be increasingly difficult for the European Union to maintain its sanctions against Syria without exemptions for the opposition.