A suicide bomber attacked a Pakistani military bus taking medical corps staff to work in the city of Rawalpindi on Monday killing at least five people and wounding 25, police and military officials said.

Violence has intensified in Pakistan in recent months with the army battling militants in the northwest and suicide bomb attacks in towns and cities, raising concern about prospects for the nuclear-armed country in the run-up to February 18 elections.

The bomb went off during the morning rush hour outside the army's National Logistics Cell in the city, where the army has its headquarters.

"The bomber was apparently on a motorcycle and rammed into a military vehicle," said a military official at the scene.

Several vehicles were badly damaged and army caps were scattered on the road at the site of the blast, about 100 metres (yards) from the back of the army headquarters compound, a witness said.

City police official Basharat Abbasi said five people were killed and about 25 were wounded, 10 seriously.

It was the seventh suicide bomb blast in Rawalpindi in the past six months.

Earlier attacks included a blast on a bus taking staff of the main military intelligence agency to work and a gun and bomb attack that killed opposition leader Benazir Bhutto as she was leaving an election rally on December 27.

Parliamentary elections, which are meant to complete a transition to civilian rule, were scheduled for early January but were postponed to February 18 after Bhutto was killed.

The government has blamed an al Qaeda-linked militant leader, Baitullah Mehsud, who is based in the South Waziristan region on the Afghan border, for the attack on Bhutto and many of the other attacks across the country.

The military has stepped up operations against Mehsud in recent weeks after his men attacked and captured a remote fort.