Police officials said the attackers chose their target because it was home to about 200 police officers [AFP]

Suicide bombers armed with guns and grenades have attacked a Pakistani police station in the northwest of the country, killing four officers, officials say.

The three attackers opened fire with machine guns, and then used hand grenades to attack the building, before detonating their suicide vests, Yameen Khan, a senior police official, said.

Khan said Friday's attack targeted the police station in central Peshawar because many officers lived there.

Pieces of human flesh and body parts, including the head of one of the suicide bombers, were scattered inside the police station, along with broken windows and chairs, an AFP reporter said.

Police officer Sattar Khan said six policemen were wounded in the attack.

Pakistani Taliban spokesman Ahsanullah Ahsan told The Associated Press news agency the attack was carried out by an affiliated group, the Abdullah Azzam Brigade.

Abu Zarar, a man who claimed to be a spokesman for the Abdullah Azzam Brigade, also told the AP that the group executed the attack.

'Three blasts'

The bombers struck at about 7:15am (02:15 GMT), when local residents were preparing to leave for work and school.

"The attackers first started firing on the gate of the police station and then used the hand grenades. Later they entered inside the police station," Imtiaz Khan, a senior police official, said.

Witnesses said that policemen were coming off night shifts when the attack took place.

"We were just trying to sleep after we finished night duty when we heard the blast," said Sayed Ali, a police constable who lives at the station.

"We ran out of the building from the back door and then there were three blasts," he said.

Officials said between 15 and 18 kilogrammes of explosives were stuffed inside the suicide vests, along with ball bearings and steel plates.

Shafqat Malik, the chief of Peshawar's bomb disposal squad, said the suicide bombers were aged between 18 and 22.

Imtiaz Altaf, the city police chief, said that the attackers aimed to "occupy the police station, but they failed".

He said the attack was likely in revenge for ongoing military offensives in the region.

Friday's attack was the latest in a series of bombings in or close to Peshawar.

On Thursday, a powerful car bomb killed 12 people and wounded dozens more at a bus stand on the outskirts of the city.