Four Pakistani soldiers were among six people killed and 18 injured in a targeted attack on army men escorting a census team by a young suicide bomber here, the latest in a series of bombings to hit the country.

The blast happened near a Cantonment area in Lahore, the provincial capital of Punjab province. "Six people including four army men have been killed in the suicide attack. Over a dozen injured have been shifted to combined military hospital (CMH) and General Hospital Lahore," Punjab government spokesman Malik Muhammad Khan confirmed.

TV footages and photographs from the scene showed two vans and a motorcycle damaged in the blast. No group has claimed responsibility for the blast so far. Khan said the area has been cordoned off and law enforcement agencies were at the site collecting evidence.

The blast struck when the army personnel accompanied a team carrying out Pakistan's first census in 19 years and launched in March. Security has been put on high alert in Lahore.

A Lahore police source told PTI the young suicide bomber came near the army vehicle on foot and then blew himself up. "The severed head of the suicide bomber has been found.

It appears that some eight to 10 kilogrammes explosives were used," the source said. An eyewitness, Taimur Shahid, said he was heading to a shop near the blast site to get groceries when he heard a loud bang metres away.

"I moved to the blast site and saw a number of soldiers lying in a pool of blood. The locals moved them to a nearby hospital. Later, rescue and army personnel reached the spot and cordoned off the area," he said.

Punjab Health Minister Imran Nazir said four of the injured were critical. He said an official of the Pakistan Air Force, who was passing by with his wife on a motorcycle at the time of blast, was among the four soldiers dead.

Lahore Corpse Commander Sadiq Ali said the people would not be cowed down by such cowardly attacks. "The war against terror will continue," he said.

Law Minister Rana Sanaullah said terrorism in Pakistan could not end till the terror camps of Jammatul Ahrar and other terror groups are not eliminated in Afghanistan.

On February 23, a suicide blast in an upscale area in Lahore killed eight people and injured 30 people. Another blast targeting police officers at a demonstration in the city in the same month killed 13 people, six of them police men. Jammatur Ahrar had claimed its responsibility.