Afghan policemen inspect the site of a suicide car bombing in Kabul, Afghanistan, on Aug. 10, 2015. In another car bomb attack Saturday Aug. 22, 2015, at least 12 people were killed, Afghan officials said.

Afghan policemen inspect the site of a suicide car bombing in Kabul, Afghanistan, on Aug. 10, 2015. In another car bomb attack Saturday Aug. 22, 2015, at least 12 people were killed, Afghan officials said. (Ahmad Massoud/Xinhua/Zuma Press/TNS)

KABUL, Afghanistan — NATO says three American contractors were among 12 people killed when a suicide car bomb struck a NATO convoy in downtown Kabul on Saturday, the latest in a string of insurgent attacks apparently aimed at demonstrating that the Taliban remain a force to be reckoned with despite the death of the movement’s founder and longtime leader.

NATO did not name the dead contractors in its statement.

At least 66 others were injured in the attack, said Wahidullah Mayar, a spokesman for the Health Ministry, in a post on Twitter. Among the casualties were women and children, he said.

The Taliban have staged a series of bombings and other high-profile attacks in Kabul in recent months aimed primarily at Afghan government institutions and international forces. Many of the attacks occurred as the two sides agreed to hold talks to explore the possibility of a peace process aimed at ending the 14-year war. But the more recent ones have come amid speculation that the movement is in disarray and experiencing a leadership crisis following news last month that its reclusive leader, Mullah Mohammad Omar, had died in 2013.

Mullah Omar was replaced by his deputy, Mullah Akhtar Mansour, but that appointment has been contested by some members of the leadership council.

Afghan government officials have dismissed the barrage of attacks as evidence of desperation among insurgents, but Afghan President Ashraf Ghani has sharply increased criticism of neighboring Pakistan over what he sees as a failure to crack down on militant groups.

Saturday’s attack on the coalition convoy occurred about 4:20 p.m. on a road leading to the airport, near a hospital. Photos from the scene showed what appeared to be armed Westerners in civilian clothes around wrecked SUV-style vehicles.

Coalition spokesman Col. Brian Tribus said in a statement that investigators were gathering information about the attack. "One Resolute Support contracted civilian was killed in the attack and two others died of wounds as a result of the attack," he said.

Habib Rahman Qasim, a doctor who works at the private hospital near the scene, said he had seen at least one dead child and one woman. He said his clinic had received 15 slightly injured civilians.

"It was a suicide attack, and the blast was huge," he said.

Coalition contractors and civilians have sustained relatively heavy casualties since the coalition declared an end to its combat mission in 2014. Saturday's attack brings this year's death toll to 16 contractors and coalition civilians. Three coalition service members have died in the same period.

On Aug. 7, eight Afghan security guards employed by a coalition contractor were killed in an attack on a military base in Kabul in one of the deadliest days of the war.

A series of attacks around the city on that day left nearly 60 people dead and hundreds injured. Since then more attacks and the kidnapping of at least one German aid worker on Monday have increased tensions in Kabul.

International aid organizations, including the German government aid agency GIZ, have reportedly evacuated many of their expatriate employees, with some relocating operations to Dubai and elsewhere.

The attacks have led Afghan officials to accuse Pakistan of not doing enough to fight the Taliban and other militant groups that train and operate across the border.

The Pentagon has threatened to withhold hundreds of thousands of dollars in aid to Pakistan over what it says is a lack of action against the Haqqani network, a Pakistan-based group, affiliated with the Taliban, that is responsible for some of the bloodiest attacks of the Afghan war.

Afghan civilians have also suffered heavily in attacks around the country. At least 1,592 were killed and 3,329 wounded in the first six months of 2015.

Zubair Babakarkhail contributed to this Twitter: @joshjonsmith

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