A man climbs between burned vehicles following the blast in Peshawar on Friday. (Fayaz Aziz/Reuters)

A suicide bomber blew up his vehicle near a crowded market in northwestern Pakistan on Friday, killing 49 people and pushing the country closer to an offensive against militants in their main stronghold along the Afghan border.

The attack, which wounded more than 100 people in Peshawar, was Pakistan's deadliest in six months and was a reminder of the ability of insurgents to strike in major cities, despite operations against them and the death of their leader in a U.S. missile strike.

The blast was heard several kilometres away and left the charred skeleton of a bus flipped on its side in the middle of the road, next to the twisted remains of a motorbike. Passersby pulled out the wounded and the dead, including a young girl wearing an orange dress who was heading to a wedding with family members.

One man staggered from the scene, his face covered with blood. People rushed to cover the bodies of victims whose clothes were burned off.

Looks like 'doomsday'

"I understood for the first time in my life what doomsday would look like," said Noor Alam, who suffered wounds to his legs and face and was at a hospital overrun with other casualties.

Peshawar police Chief Liaqat Ali Khan said the attacker was in a car packed with a "huge" amount explosives and artillery rounds. There was no claim of responsibility for the bombing, the target of which was not immediately apparent. Militants typically attack government, military or Western targets, but blasts have taken place in public places before.

Zafar Iqbal, a doctor at the main Peshawar hospital, said 49 people were killed and more than 100 wounded. Seven children were among the dead.

"I pray to Allah, please destroy all these people who are killing the innocents," said Sher Akbar from his hospital bed. "People were crying. They were in pain. I thought we were all dying."

U.S. pushes Pakistan for action

The United States is pushing Pakistan to take action against insurgents using its soil to fuel the insurgency in neighbouring Afghanistan. The army has carried out some offensives in the northwest this year, killing many militants and earning it measured praise in the West, but the insurgents have responded with scores of suicide attacks.

The army has confirmed it is prepared to launch a major offensive in South Waziristan, a region along the Afghan border considered the fountainhead of suicide attacks and other militant activity in Pakistan. It has not given a date for the launch.

Interior Minister Rehman Malik said the attack meant the country now "had no other option but to carry out an operation in South Waziristan."

"We will have to proceed," he told a local television station. "All roads are leading to South Waziristan."

The bombing came just days after a Taliban suicide attacker evaded tight security to kill five people at the office of the UN's World Food Program in the capital, Islamabad, and two weeks after another explosion killed 11 in another part of Peshawar.

Malik said authorities had arrested a man alleged to have been the "handler" of the UN bomber. He gave no more details.

Also Friday, militants ambushed a tanker carrying fuel for U.S. and NATO forces in Afghanistan at a gas station near Peshawar, torching it, said Fazal Rabi, a police official. No deaths or injuries were reported in the attack, which highlighted the vulnerability of the American-led mission in landlocked Afghanistan as Washington debates sending more troops.

Pakistani Taliban have often targeted U.S. and NATO supply convoys passing through northwest Pakistan for Afghanistan, though there have been fewer attacks reported recently. Most of the non-military supplies for foreign troops in Afghanistan are unloaded at the Karachi seaport and are then trucked in through the northwest.

Pakistan's army has launched three operations in South Wazirstan since 2001 but each time has been forced to abandon the push amid fierce resistance. U.S. missile strikes and Pakistani mortar and jet bombings have hit targets there over the last year, but no ground operations have been launched.

One such U.S. attack in the region in August killed Pakistani Taliban chief Baitullah Mehsud. The group has since named a new leader, Hakimullah Mehsud. He has threatened suicide attacks and said his men were preparing to repel any push into South Waziristan.