Consequences of chemical attack huge, Assad told

Mr Ban also suggested he would not favour an asylum deal for the Syrian leader as a way to end the country’s civil war and cautioned the United Nations does not allow anyone “impunity”.

The UN chief was speaking as battles between gunmen loyal to opposite sides in neighbouring Syria’s civil war raged in the streets of a northern Lebanese city where two days of clashes have killed at least six people and wounded more than 50.

The Lebanese army fanned out in the city of Tripoli in an attempt to calm the fighting, with soldiers patrolling the streets in armored personnel carriers and manning checkpoints. Authorities closed major roads because of sniper fire.

The Syrian crisis has spilled over into Turkey, Israel and Jordan over the past 20 months, but Lebanon is particularly vulnerable to getting sucked into the conflict. The countries share a complex web of political and sectarian ties and rivalries that are easily enflamed. Lebanon, a country plagued by decades of strife, has been on edge since the uprising in Syria began, and deadly clashes between pro- and anti-Assad Lebanese groups have erupted more than a dozen times.

The fighting comes at a time of deep uncertainty in Syria, with rebels fighting government troops near Assad’s seat of power in Damascus.

“I again urge in the strongest possible terms that they must not consider using this kind of deadly weapons of mass destruction,” said Mr Ban, speaking on the sidelines of the climate conference in Qatar.

“I have warned that, if in 
any case this should be used, 
then there will be huge consequences. And they should be accountable,” he said of the Syrian regime.

Syria is believed to have hundreds, if not thousands, of tons of chemical agents, including mustard gas, a blistering agent, and the more lethal nerve agents sarin and VX, experts say.

The Assad regime has said it would not use such weapons on its own people even if it had them. Syria is party to the 1925 Geneva Protocol banning chemical weapons in war.

US intelligence has seen signs that Syria is moving materials inside chemical weapons facilities recently, though it is unsure what the movement means. Nevertheless, US officials said the White House and its allies are weighing military options should they decide to secure Syria’s chemical and biological weapons.

The UN chief’s warnings came as fighting around the Syrian capital, Damascus, was closing in on Mr Assad’s seat of power. Clashes between rebels and regime troops have intensified in the suburbs around the city in recent weeks. The area has been a stronghold of predominantly Sunni Muslim rebels, who are fighting to topple Mr Assad’s regime, dominated by Alawites, an offshoot Shiite group.

The increased pressure of the opposition fighters on the capital has raised fears that Mr Assad or his forces will resort to desperate measures, perhaps striking neighbours Turkey or Israel, or using chemical weapons.

Syria’s uprising began with peaceful protests in March 2011 and later escalated into a civil war that the opposition says has killed more than 40,000 people. So far, both sides have refused international calls for a negotiated solution.

In Brussels, US Secretary of State Hillary Rodham Clinton reiterated concerns that “an increasingly desperate Assad regime might turn to chemical weapons” or lose control of them to militant groups. She also said Nato’s decision on Tuesday to send Patriot missiles to Turkey’s southern border with Syria sends a message that Ankara is backed by its allies. The missiles are intended only for defensive purposes, she said.