Many of those injured, in the latest of the string of suicide bomb attacks in Pakistan, are said to be critical [EPA]

A suicide bomb attack has killed at least 18 people and injured 35 others in the town of Kohat, in northwest Pakistan.

A suicide bomber blew himself up on Wednesday, in Tira, the main bazaar of the garrison town, also damaging 30 shops.

Fazal Naeem, a police spokesman said that the bomber approached the door of a bus carrying passengers to Orakzai, a nearby tribal district, and detonated his explosives.

The injured have been shifted to hospital.

Al Jazeera's correspondent, Zeina Khodr, reporting from Islamabad said that, "many of the injured are critical so we can't rule out the death toll going up."

Dilawar Bangash, Kohat police chief said that the target of this attack was not immediately clear as the victims were both Sunni and Shia Muslims.

"A boy between the ages of 18 and 20, who was carrying about 6 kg [13 lbs] of explosives, carried out the attack. We have found the head and legs of the suicide bomber," he added.

No group has yet claimed responsibility for this attack.

Kohat is situated close to Pakistan's border regions with Afghanistan, which is a stronghold of Taliban fighters.

The blast in Pakistan, the third in as many days, is part of a new wave of bombing after a brief lull. Pakistan army has responded with military offensives in some parts of the northwest.

"Everytime the army launches a major offensive, the Taliban strike back," our correspondent said.

"It is very difficult to stop suicide bombers, it is an ongoing war so the Pakistan Army is engaging local elders for support against the Taliban."

On Tuesday a suicide bomber targetted the chief minister of Pakistan's southwestern province of Baluchistan, damaging his motorcade but leaving the minister unhurt, officials said.

On Monday, 50 people were killed in two blasts at a government compound in Mohmand, also in the border area.

Around 4,000 people have died in suicide and bomb attacks across Pakistan since government forces raided the Red mosque in Islamabad in 2007.

The attacks have been blamed on networks linked to the Taliban and Al-Qaeda.