And they wouldn’t think twice about using them.

BEIRUT – A Syrian rebel offensive aimed at easing a government siege east of Damascus has brought fighting closer to the last declared stockpile of President Bashar Assad’s chemical weapons, according to diplomats and activists.

Syria has been removing 1,300 tons of chemical weapons under a deal reached last year which averted Western military strikes, after a sarin gas attack on rebel-held suburbs around the Syrian capital in August.

But it has missed several deadlines to ship out the toxins – the last of which was April 27 – and has told the international mission overseeing the operation that one remaining chemical site remains difficult to reach because of the fighting.

Activists say rebels have clashed with Assad’s forces between Dumair air base, which they said came under heavy rocket fire from the rebels, and Sayqal air base about 40 km (25 miles) further east where the chemicals are believed to be held.

While the rebel attack appears more focused on Dumair and on breaking the military stranglehold which Assad’s forces have imposed closer to the capital, the fighting has increasingly isolated Sayqal and encroached towards it.

Activists said the fighters are from the Islamic Front – one of the largest and most powerful Islamist rebel coalitions – the Rahman Corps and Ahmad Abdo Brigades. The offensive appeared to be funded by Gulf Arab supporters, they said.

The diplomat said rebels have overrun the abandoned and emptied chemical base at Khan Abu Shammal, which lies between Dumair and Sayqal, and cut the road linking them.

He described the proximity of the fighting to Sayqal as worrying and said it was not clear whether there were alternative routes to evacuate the chemicals other than the road which was blocked by the rebels.