United States President Barack Obama has urged President Bashar al-Assad of Syria not to make use of his stockpile of chemical weapons to strike at his enemies.
Damascus has implied it could use them against an attack by foreign forces.
That, said Mr Obama, would be a tragic mistake.
''They will be held accountable by the international community and the United States, should they make the tragic mistake of using those weapons," he said.
UN Secretary General Ban Ki-moon said that any thought of using chemical weapons would be "reprehensible".
In addition, Israeli Prime Minister Benyamin Netanyahu spoke of a "great threat" of weapons sites falling into the hands of the Hizbollah group in Lebanon, which is allied to President Assad.
