A car bomb targeting a convoy carrying civilian NATO contractors killed 12 people outside a Kabul hospital on Saturday, part of a wave of attacks in the capital since news broke last month of the death of Taliban leader Mullah Omar.
Scores were wounded in the suicide attack on a busy residential street. Three of the dead were foreigners.
The powerful blast destroyed several vehicles, including a school van and an armored pick-up truck which was left twisted and blackened, with another car in flames. Paramedics carried away casualties on stretchers.
"Twelve dead bodies and 66 wounded people were taken to several Kabul hospitals," health official Kabir Amiry said. "Some were in a bad condition."
In a statement the Taliban denied it was behind the attack. No group has claimed responsibility.
Minutes after the explosion, British and U.S. soldiers arrived at the scene in armored vehicles. Several armed security contractors also pulled up and ran to the blast site.
"One Resolute Support contracted civilian was killed in the attack and two others died of wounds," said Brian Tribus, a spokesman for the U.S.-led NATO mission known as Resolute Support. He did not say what nationalities the dead were.
Security sources said the contractors worked for DynCorp International. The company, which provides training, security and aviation maintenance to the NATO mission and the Afghan military, did not immediately respond to a request for comment
Bombings have increased in Kabul since the government and the Taliban in July confirmed that Mullah Omar had died two years ago. Some analysts say the insurgents are trying to show they remain potent.
The Taliban is fighting to overthrow the foreign-backed government, expel foreign forces from Afghanistan and impose a strict interpretation of Islamic law.
The violence has put paid to hopes that new leader Mullah Mansour would quickly return the insurgents to the negotiating table. Instead he seems set on consolidating his position in the group that ruled for six years until the 2001 U.S. invasion.
A massive truck bomb that leveled houses, an explosion at the gate to Kabul airport and attacks on U.S. special forces and Afghan police cadet bases killed dozens of people this month.
Elsewhere in Afghanistan, the group has regained ground in parts of Helmand province since British and U.S. combat forces it battled there left last year. It has also advanced in districts in the north but has struggled to hold ground.
The violence has strained ties with neighbor Pakistan, with Afghan President Ashraf Ghani accusing the Pakistan government of not doing enough to stop militants planning attacks from training camps he says lie across the border.