A suicide bomber on Thursday rammed his explosive-laden motorcycle into a bus carrying Pakistan Air Force personnel, killing eight of them and injuring 40 others, in the second such attack this week in Punjab province.

Officials said the attack took place in the Mitha Masoom area near the Sargodha airbase, a key facility of the PAF where its frontline F-16 fighters are based, 200 km from Islamabad.

Interior Ministry spokesman Javed Iqbal Cheema said eight Air Force personnel were killed in the attack. These included a flying officer, four squadron leaders and three civilian employees of the PAF.

The blast triggered a fire in the bus, which was on a routine trip to ferry PAF personnel to a training facility, he said.

Police said they had found the head and other body parts of the attacker.

Three schoolchildren were among the injured. They were in a school bus which was also hit by the blast. The injured, many of them with severe burns, were rushed to nearby hospitals. Announcements were made on loudspeakers for people to donate blood for the injured.

Security forces cordoned off the area soon after the blast while investigators and forensic experts scoured the site for clues.

This was the second suicide attack on Pakistan's armed forces since October 30, when a bomber blew himself up near the residence of Gen Tariq Majid, the chairman of the joint chiefs of staff committee, in the high-security cantonment area in Rawalpindi, killing seven people.

A suicide attack was foiled in Sargodha a few month ago when police shot dead a bomber who had sneaked into a police compound before he could blow himself up.

Rawalpindi and Islamabad have been on red alert since October 27 following intelligence reports that suicide bombers had entered the twin cities to carry out attacks.

Military spokesman Maj Gen Waheed Arshad said "necessary precautions" would be taken to prevent further attacks on armed forces personnel.

Nearly 140 people were killed and hundreds injured in a suicide attack on former premier Benazir Bhutto's [Images] homecoming motorcade in Karachi on October 19.

The government had ordered authorities to beef up her security in the wake of the attack in Rawalpindi.

Extremist violence has escalated in Pakistan since the July storming of Lal Masjid in Islamabad by military to flush out Islamic militants.