MINGORA, Pakistan (AP) – A suicide attack on a prison van in northwest Pakistan wounded at least 10 policemen Saturday, while troops waging an offensive in a nearby tribal region killed 20 suspected Taliban insurgents, authorities said.

A car bomber targeted the van as it arrived at a jail in Timergarah, before it picked up prisoners to take to nearby Swat Valley, senior police official Shakeel Khan said. No prisoners were in the van at the time.

Two of the victims were in critical condition and were shifted to the main northwest city of Peshawar, the police official said.

Timergarah is in deeply conservative Lower Dir district, which is near the Afghan border. It was a militant stronghold until spring 2009 when a military offensive there and in Swat reclaimed the areas from insurgents.

Sporadic violence still occurs. Pakistan followed that offensive with one in South Waziristan tribal region, the main stronghold of the Pakistani Taliban.

Many militants there have since fled to other areas such as Orakzai, another part of the lawless tribal belt bordering Afghanistan, leading the army to open new fronts.

Troops on Saturday raided a militant ammunition depot in Sangra village of Orakzai, killing 10 alleged insurgents, local administrator Jehanzeb Khan said. One soldier was wounded. Airstrikes later destroyed three more hide-outs, killing another 10 suspects, Khan said.

The information is nearly impossible to verify independently, access to the tribal belt and regions such as Dir is difficult to obtain due to the dangerous, remote nature of the terrain and legal restrictions.