Nine Pakistan army soldiers were killed and four others injured when a suicide attacker blew himself up near a group of recruits in Kohat cantonment in the North West Frontier Province on Monday.

The blast occurred as the recruits were returning to the cantonment after participating in a sports event. The suicide bomber got close to the personnel and detonated his explosives on a road that is also used by the local people, military spokesman Major General Waheed Arshad said.

An army battalion headquarters and an army public school are also located in the area, some 50 kilometres from the provincial capital of Peshawar.

Arshad said it appeared the recruits were the main target of the bomber. "The recruits were coming back from playing a match when the suicide bomber blew himself up close to them on the road," he said.

Asked how such an attack was carried out in a high-security area, Arshad said, "This is a public road on which there was other traffic. It's very difficult to identify a suicide attacker unless you have prior information. It's a difficult thing to prevent".

No group claimed responsibility for the attack, the latest in a series of suicide bombings targeting Pakistan's armed forces.

On Saturday, two soldiers and three civilians were killed in a suicide attack in Nowshera district. Twin suicide attacks within the cantonment near the southwestern city of Quetta killed five soldiers and injured 22 people on December 13.

The suicide attacks have increased since the Pakistan army carried out an operation in July to flush out militants holed up in the Lal Masjid in Islamabad. At least 100 people were killed in that action.

Pro-Taliban militants targetted by the army in the Swat valley of NWFP have also threatened to carry out suicide attacks against the security forces.