A car bomb hit a Pakistani refugee camp Thursday, killing 13 people including women and children, raising further fears for the security of a May general election in the nuclear-armed state.

More than 30 other people were wounded when the bomb exploded in Jalozai, the largest refugee camp in Pakistan, as scores of people queued for rations handed out by a local charity in partnership with the United Nations and USAID.

Jalozai is home to tens of thousands of displaced people from the tribal belt, a stronghold of the Taliban and Al-Qaeda-linked militants, on the Afghan border and is close to the main northwestern city of Peshawar.

There was no immediate claim of responsibility but officials linked the attack to fighting in Khyber district, where the military has stepped up an offensive against Taliban and local militia, and from where most camp residents have fled.

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

District police chief Mohammad Hussain said the bomb was detonated on a timer, and carried up to 35 kilograms of explosive and mortar shells.

An AFP reporter saw scenes of devastation. Pieces of human flesh and blood spattered the scene. Slashed bags of rations marked USAID, the US government's agency for international development, and WFP, the UN food programme.

Spilt grain and children's food supplements littered the ground next to discarded toys, sandals and twisted metal. The engine of the car which exploded lay around 50 feet from a two-foot crater left by the blast.

Tariq Khan, a 40-year-old displaced driver from Khyber, said he was in his tent when he suddenly heard a "very loud" blast and saw thick black smoke outside.

"I rushed to the spot and saw bodies lying in a pool of blood and wounded people crying in pain. I saw small pieces of human flesh everywhere and found my uncle, whose both legs had gone, and he was crying with pain," Khan told AFP.

"I lifted him and looked for a car and luckily found one nearby and took him to hospital," he said.

Jehanzeb Khan, 27, another refugee from Khyber, also spoke about helping to rescue the wounded.

"I saw bodies, blood and wounded, everywhere. I started lifting the wounded and put them in the cars and ambulances and the white clothes I put on this morning turned all red with blood," Khan told AFP.

Local administration official Ayaz Khan Mandokhel said 13 people were killed, including two children aged around eight and 10, and three women.

"Some 36 others were wounded," he told AFP.

Mohammad Ashraf, project director at Pakistani charity BEST, a UN partner, said a 30-year-old female member of staff who worked on hygiene was killed. Nine other members of staff who were distributing food were wounded, he said.

Aside from the election, the bombing will raise concerns about the safety of aid workers in the northwest, where seven charity staff were shot dead on January 1 and where those working on polio eradication have also been targeted.

Most of those now in Jalozai, built originally to host Afghan refugees, come from Khyber, where the army is fighting to dislodge the Taliban from the Tirah valley in an effort to safeguard the election and to crack down on militants behind a wave of attacks.

The May 11 vote will mark the first time that an elected civilian government hands over to another in a country that has seen three military coups and four military rulers since partition from India and the end of British rule in 1947.

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.

A parliamentary committee has until Friday to select a candidate to head a caretaker administration, which will guide the country through the campaign period.

An election schedule, which will fix dates for candidates to file nomination papers, be screened and for objections to be raised, is also due to be unveiled in the next few days, formally launching the electoral campaign.