Rescue worker survey a damaged vehicle after it was hit during a bomb attack in Peshawar September 3, 2012. Two Americans working for the U.S. consulate were wounded in a bomb attack on their vehicle in the Pakistani city of Peshawar on Monday, the American embassy said. REUTERS/Fayaz Aziz

Peshawar, Pakistan - A suicide car bomber struck a US consulate vehicle in Pakistan on Monday, killing four people in the deadliest attack targeting Americans for two years in the frontline state in the war on Al-Qaeda.

The US State Department said no American consulate personnel were killed, but a regional Pakistani cabinet minister insisted two Americans were among the dead.

Up to 19 people were wounded when the bomber struck during the morning rush hour in the northwestern city of Peshawar, near the office of the UN Refugee Agency (UNHCR) and residential quarters used by the US consulate.

There was no immediate claim of responsibility, but it was at least the third time that the consulate and its staff have been targeted by militants linked to the Taliban and Al-Qaeda since April 2010.

The US State Department said a consulate vehicle was hit in an apparent terrorist strike but said no US consulate staff were killed.

Spokeswoman Victoria Nuland said two Americans and two Pakistanis working for the mission were receiving medical treatment for their wounds, and that the United States was “seeking further information about other victims”.

But Mian Iftikhar Hussain, information minister for Pakistan's Khyber Pakhtunkhwa province, said four people were killed, two of them Americans.

When asked to comment on the US statement, Hussain said: “What can I do if they are denying? Police confirmed to me that two of the dead were American diplomats.”

Pakistani security officials told AFP that the US vehicle was the target and a half-burnt US passport was recovered from a vehicle after the attack.

Peshawar police chief Imtiaz Altaf said 19 people were wounded in the blast and that the bomber's vehicle had been packed with up to 110 kilogrammes (240 pounds) of explosives, including more than 10 mortar shells.

An AFP reporter saw two dead bodies in a hospital morgue, one of which was burnt beyond recognition. The other appeared to be of a local resident.

Police said they believed the two bodies belonged to passers by.

Mohammad Sadid, 35, said he was driving to work at his pharmacy when he heard a deafening blast on the opposite side of the road in University Town neighbourhood.

“It was so powerful that it jolted my car with a massive jerk. My head banged the steering wheel and the wind shield. I couldn't understand what had happened. I saw a car on fire. It became a large fireball,” he told AFP.

The explosion left a crater in the road, damaged vehicles and demolished the facing walls of four nearby houses, an AFP reporter said.

Hussain called the bombing “a dangerous move from the terrorists”, adding that “they want to terrorise the foreigners”.

Taliban and Al-Qaeda-linked militant groups who are sworn enemies of the United States frequently carry out attacks and have strongholds in the nearby tribal belt.

They have vowed to avenge American drone strikes targeting Islamist militants in Pakistan's semi-autonomous tribal areas and thwart a rumoured prospective Pakistani offensive in North Waziristan.

Although Islamabad is an ally of Washington, relations dramatically worsened after a CIA contractor killed two Pakistanis in the eastern city of Lahore and US special forces found and killed Osama bin Laden in Pakistan last year.

The United States is currently weighing up whether to blacklist as terrorists the Al-Qaeda-linked Haqqani network, whose leaders are understood to be based in Pakistan, in a move that could further damage already fraught ties with Islamabad.

The United States heads around 130 000 NATO troops in Afghanistan but is preparing to hand over security responsibility to Afghans by the end of 2014.

Anti-American sentiment in Pakistan has increased since Islamabad agreed in July to end a seven-month blockade on NATO goods crossing into Afghanistan. The blockade was imposed after botched US air strikes killed 24 Pakistani soldiers last November.

On Monday, gunmen in southwestern Pakistan attacked three NATO supply trucks, injuring three drivers and torching two of the lorries, police said.

In May 2011, a Taliban bomb damaged a US consulate vehicle and wounded two US government employees in Peshawar just days after American commandos killed bin Laden in a raid on his Pakistan hideout.

In April 2010, a Taliban gun, grenade and double suicide car bomb attack on the consulate killed five Pakistanis but failed to penetrate the compound.

In February 2010, three American military personnel were among eight killed in a bomb attack at the inauguration of a renovated girls' school in the northwestern district of Lower Dir. - Sapa-AFP