KABUL: At least 12 people including three Nato contractors were killed Saturday when a suicide car bomber struck a foreign forces convoy, officials said, underlining the precarious security situation in the Afghan capital.

No group immediately claimed responsibility for the blast, which struck outside a civilian hospital in Kabul following a wave of fatal bombings earlier this month that rattled the city.

The piercing explosion in a residential Kabul neighbourhood reverberated around the city and left a trail of devastation, with an AFP photographer seeing the mangled wreckage of a burning vehicle at the scene of the attack.

A foreigner was among 12 people killed in the blast, with 66 others – including women and children – wounded, health ministry spokesman Wahidullah Mayar said on Twitter.

He did not give the nationality of the foreigner.

Senior health official Sayed Kabir Amiri confirmed the toll from the attack, which comes as Taliban insurgents escalate their annual summer offensive against the US-backed Afghan government.

“One Resolute Support (Nato) contracted civilian was killed in the attack and two others died of wounds as a result of the attack,” Nato said in a statement, without specifying their nationalities.

Fraidoon Obaidi, the head of Kabul's Criminal Investigation Department, said officials were investigating the bombing.

Nato officials did not immediately comment on the blast, which prompted the heavily-fortified US embassy, located a few kilometres (miles) away in the centre of Kabul, to sound its emergency sirens and a “duck and cover” alarm warning.

US-led Nato forces ended their combat mission in Afghanistan in December last year, although a 13,000-strong residual force remains for training and counter-terrorism operations.

Saturday's blast comes amid heightened security in Kabul after a wave of bombings earlier this month that killed more than 50 people and wounded hundreds, prompting fury from President Ashraf Ghani who blamed Pakistan for failing to rein in Taliban insurgents.

The Taliban are stepping up their summer offensive, launched in late April, amid a bitter leadership dispute following the announcement of the death of longtime leader Mullah Omar.

Mullah Akhtar Mansoor, Omar's longtime trusted deputy, was named as the new Taliban chief in late July in an acrimonious power transition.

Al Qaeda chief Ayman al-Zawahiri recently pledged his group's allegiance to Mansour, in a move which could bolster his accession amid the growing infighting within the Afghan militant movement.

The latest wave of deadly violence underscores Afghanistan's volatile security situation amid a faltering peace process.

The first face-to-face talks between the Afghan government and the Taliban took place last month in the Pakistani hill town of Murree, aimed at ending the 14-year insurgency.

The Taliban distanced themselves from a second round of talks that were scheduled for the end of July after the announcement of Omar's death.