Previous terrorist attacks have taken various forms, including vehicle bombs, hand grenades and small, improvised bombs.

The Qurna blasts involved two vehicle bombs, one in a minibus in a bus terminal, the other in a car beside a nearby market.

"We've notified security directors to secure HVAC systems, and parking garages in particular, because of concerns about a vehicle bomb," he said.

He was present at the Al Husseini building, where vehicle bombs were readied.

Methods of attack include shootings, bombings, suicide bombs, vehicle bombs, rockets and mortars.

In Connecticut, a vehicle bomb went off at a festival in New London.

Insurgents often conceal themselves in the rest of the population and may employ vehicle bombs and suicide bombing.

At least 61 people were killed and many more wounded in a three-pronged attack there on Feb. 12 involving two vehicle bombs and a roadside bomb.

A Hamas armored personnel carrier confiscated from Palestinian Authority security forces managed to knock a hole through the fence, allowing two vehicle bombs to enter.

Terrorists with multiple vehicle bombs.