US President Barak Obama has warned Syrian leader Bashar Assad it would be a "tragic mistake" to unleash chemical weapons. His warning came after Damascus admitted it has a stockpile and will use them if attacked. The warning, a first admission by the Syrian regime that it has weapons of mass destruction, came as regime troops reclaimed control of most of Damascus after a week of heavy clashes. Fighting was still raging in the country's second city of Aleppo, where rebels claimed to have captured several districts. Activists said at least 52 people, including 24 civilians, were killed in violence across Syria yesterday. At a Damascus news conference on Monday, the Syrian foreign ministry spokesman Jihad Makdi said Syria has chemical weapons and will use them if attacked by outsiders, though not against its own civilians. Obama responded that given the regime's stockpile of chemical weapons, the US will continue to make it clear to Assad and those around him that the world is watching.