ISABELA, Philippines – A powerful booby trap bomb wounded 22 soldiers, seven of them critically, as they patrolled a former stronghold of al-Qaeda-linked militants Tuesday (April 10th), local army commander Colonel Ricardo Visaya told AFP.

The soldiers were patrolling the outskirts of a remote camp captured last month from Abu Sayyaf extremists when the device went off. The Abu Sayyaf had formerly used the camp on the southern island of Basilan to hide many of their kidnap victims until a large military assault dislodged the rebels in March, Visaya said.

Helicopters were deployed to airlift the wounded to a military hospital, Visaya said.

The group has been blamed for the worst terror attacks in Philippines history and has frequently resorted to kidnapping to raise funds, often targeting foreigners.

Seven foreigners -- a Dutchman, a Swiss national, an Australian, two Malaysian traders, an Indian and a Japanese man -- are believed to still be held by the Abu Sayyaf and other outlawed groups in the south.