Syrian rebels are closely monitoring the regime's chemical weapons sites but do not have the means to seize and secure them, their newly elected military commander has told the Associated Press.

General Salim Idris, who defected from the Syrian army in July, said he is "very afraid" that a cornered Syrian President Bashar Assad will unleash such weapons on his own people.

Syria is said to have one of the world's largest chemical arsenals. Earlier this week, Syria's UN ambassador said the regime would not use such weapons under any circumstances. However, recent US intelligence reports indicated the regime may be readying chemical weapons and could be desperate enough to use them.

Gen Idris, a 55-year-old German-trained electronics professor, was chosen as chief of staff earlier this month by several hundred commanders of rebel units meeting in Turkey.

With the election of Gen Idris and a 30-member military command centre, Syria's opposition hopes to transform largely autonomous groups of fighters into a unified force. The reorganisation came after Syria's political opposition won international recognition this month as the sole representative of the Syrian people.

Gen Idris said the rebels could defeat the regime within a month if supplied with anti-aircraft weapons. Mr Assad's troops are stretched thin and have lost ground in recent months, particularly in north-western Syria, but have kept rebel fighters pinned down with massive air bombardments.

The West has refused to supply Syria's opposition with weapons for fear they could fall into the hands of Islamic militants among the rebels, such as the al Qaida-inspired Jabhat al-Nusra, which was designated a terrorist group by the US last week.

Gen Idris estimated that about a fifth of al-Nusra's fighters are foreigners, but said he believes they will leave Syria once the regime has been toppled. He said the Syrians in the group, which is believed to number several hundred fighters in all, could be brought back to a more mainstream Islam after the war.

"They are not terrorists," he said of al-Nusra, adding that the group chose not to be part of the rebel command. He said rebel fighters are trying to monitor the chemical weapons sites. "We know exactly where they are and we are watching everything," Gen Idris said. "But we don't have the capability to put them under our control."

The West has shown little desire to intervene militarily in Syria's conflict, but US President Barack Obama has said the regime's use of chemical weapons against the rebels would be a "red line".