Pakistani authorities say militants have ambushed an ambulance in a tribal area near the Afghan border, killing six people.

Officials say gunmen fired on the ambulance Thursday as it was taking people to a health meeting in the Kurram tribal region. The motive for the attack was not immediately clear.

In another development, Pakistani police said Thursday they have arrested two militants suspected of involvement in recent suicide bombings in the city of Lahore.

The attacks targeted a naval college earlier this month and police guarding a high court building in January. At least 28 people were killed.

Also Thursday, Pakistani authorities rearrested an alleged al-Qaida militant accused of involvement in a bomb attack against former opposition leader Benazir Bhutto last October.

A court in Karachi ordered prison officials to release Qari Saifullah Akhtar on Wednesday for lack of evidence.

But the court also ruled that he must make himself available for further questioning if sufficient evidence is found.

Ms. Bhutto accused Akhtar of plotting the double suicide bombing at her homecoming parade in Karachi last October that killed about 140 people.

She made the accusation in a book written before her assassination on December 27 in a gun and bomb attack in Rawalpindi.

Pakistani authorities also accuse Akhtar of attending al-Qaida training camps in Afghanistan before the fall of the Taliban in 2001.

Some information for this report was provided by AP and Reuters.