Three U.S. contractors were among those killed by a Kabul bomb that targeted their NATO convoy, the U.S.-led coalition said, making the attack that killed 12 people one of the most lethal for U.S. citizens in Afghanistan in recent years.
The blast destroyed several vehicles, including a school van and an armored pick-up truck belonging to contractor DynCorp International which was left twisted and blackened.
"One Resolute Support U.S. contractor was killed and two Resolute Support U.S. contractors died of wounds," the NATO coalition known as Resolute Support said in a statement late on Saturday.
The suicide attack outside a hospital on a residential street at rush hour killed mainly Afghan civilians and injured scores more, heightening the anger felt in Kabul after a string of deadly blasts this month that killed dozens.
Bombings have increased in Kabul since the government and the Taliban in July confirmed that its leader Mullah Omar had died two years ago, putting paid to hopes that the insurgents would quickly return to the negotiating table.
The violence has strained Afghanistan's ties with Pakistan, with Afghan President Ashraf Ghani accusing the neighboring country of not doing enough to stop militants planning attacks from training camps that he says lie across the border.
"We will do everything to protect our people and our country and go after terrorists and our enemies anywhere they are," Afghanistan's chief executive officer Abdullah Abdullah, who shares power with Ghani, said on Sunday.
The Taliban, fighting to re-establish hard-line Islamist rule more than 13 years after the U.S.-led military intervention that toppled their regime, denied they was behind the attack. No group has claimed responsibility.
The U.S. embassy in Kabul condemned the bombing.
"The United States remains committed to assisting our Afghan partners in their efforts to ensure a peaceful future," it said in a statement.
The official anger has spilled on to the streets, with protests against Pakistan's alleged involvement in the recent bloodshed, including people burning the Pakistani flag and a campaign to boycott Pakistani products.
Security sources said the contractors worked for DynCorp International, a U.S. company. The company, which provides training, security and aviation maintenance to the NATO mission and the Afghan military, confirmed it was the target.
"A DynCorp International vehicle carrying members of our team was tragically attacked," it said in statement, without giving any additional details.