Reuters reports: On Sunday, September 29, President Bashar al-Assad declared to the world, via an interview on Italian television, his resolve to clear Syria of chemical weapons – accepting a Russian-brokered deal to avert punitive U.S. action.

That same morning his forces appear to have dropped some of the most powerful conventional weapons yet used in the civil war, in the rebel-held town of Raqqa. Evidence at the scene and witness testimony led Human Rights Watch to conclude that the 14 dead, many of them children, were killed by “vacuum bombs”.

As his government works with U.N. inspectors to destroy its chemical weapons, the scale of Assad’s remaining arsenal – and faltering supplies to his enemies – suggest he need not fear giving up poison gas shells of the kind that killed hundreds in rebel areas two months ago and prompted threats from Washington.

Relative armed strength is hard to estimate and is only one factor that may decide a war that has divided Syria on sectarian lines and drawn in rival foreign powers. But Assad’s use of such powerful weaponry while international attention is on his chemical disarmament underlines the difficulties facing the rebels – and their Western allies who want to force him out.

Air traffic data suggesting Qatar may have stopped shipping arms to Assad’s opponents, and other evidence of supply problems for the rebels despite a U.S. pledge to help, may also help explain recent government gains. Western fears of Islamists in rebel ranks complicates efforts to arm other opposition groups.

“As worries grow over Islamist influence, the rebels seem to be struggling more than they were to get supplies,” said David Hartwell, an analyst at IHS Jane’s. “At the same time, the government are throwing in everything they’ve got.”

Thermobaric or fuel-air explosives, known as vacuum bombs, are a small but fearsome part of the conventional array of artillery, tanks and aircraft Syrian troops have deployed since hostilities broke out in the wake of street protests in 2011.

Like much of Assad’s equipment, experts believe the bombs that hit Raqqa were Russian-made. Similar to devices in U.S. stocks, they detonate a cloud of vapor above the ground with a massive blast that sucks in oxygen from a wide area. That kills people in a variety of ways, including by rupturing their lungs. [Continue reading…]