A car bomb tore through a refugee camp in northwest Pakistan Thursday, killing at least 12 people and wounding 30 others, in the latest in a wave of attacks ahead of general elections in May.

The bomb went off at the Jalozai refugee camp close to the city of Peshawar, which is home to people fleeing unrest in tribal districts bordering Afghanistan that are a stronghold of Taliban and Al Qaeda-linked militants.

Live television footage showed ambulances taking the victims to hospital. The bomb left a crater and police were sifting through the wreckage of mangled cars to collect evidence.

District police chief Mohammad Hussain gave the casualty figures. Local administration official Ayaz Khan Mandokhel confirmed the casualties and said that the bomb was planted in a Suzuki Alto car.

"The death toll has risen to 12 and there are more than 30 others who were wounded," Hussain told AFP.

Hussain giving initial toll earlier had said four people were killed and 18 others were wounded.

Fuad Khan, police official responsible for security of the camp, said: "The bomb exploded in a car parked near the administration office where refugees had lined up to get ration and new arrivals were being registered."

"Several camps in the vicinity of administration office were also ripped off by the bomb blast," Khan told AFP.

"I saw about 20 casualties around me as the smoke and dust cleared, but cannot say how many were dead and wounded," Khan said.

Jalozai, an enormous camp that once hosted Afghan refugees, now houses Pakistani tribesmen fleeing unrest in the Khyber, Bajaur and Mohmand tribal districts.

Pakistan is stepping up an offensive to dislodge the Taliban from a key stronghold in an effort to safeguard general election slated for May and crack down on militants behind a wave of attacks.

The northwestern Tirah Valley, hemmed in by steep mountains and replete with numerous caves, has offered Pakistan's umbrella Tehreek-e-Taliban a new base in the tribal district of Khyber beyond the reach of ground troops.

Elections on May 11 are billed as Pakistan's first democratic transition between one elected civilian government and another, but concerns about security are casting a shadow over preparations.

The campaign also marks the first time that parties are allowed to contest the vote in the tribal belt, a reform introduced by the outgoing government in a bid to clamp down on militancy.

Security has declined markedly in Pakistan since the last election in 2008. During that campaign, former prime minister Benazir Bhutto was assassinated at a rally in Rawalpindi, an attack blamed on the Pakistani Taliban.

Officials link some recent attacks to Khyber and fear that Tirah could pose an ongoing threat as the electoral campaign heats up.