U.S. troops assess the damage to an armored vehicle of the NATO-led military coalition after a suicide attack in Kandahar province, Afghanistan, on Aug. 2. (Ahmad Nadeem/Reuters)

Two American service members were killed Wednesday when a suicide bomber in a pickup truck attacked a NATO convoy that was returning to base from a mission in the southern city of Kandahar, U.S. military officials said.

The identities of the service members were not immediately released.

A spokesman for the Taliban insurgents claimed that the group carried out the assault and that 15 foreign soldiers were killed. He also said that two armored vehicles were destroyed. He named the driver of the truck as Asadullah Kandahari and called him a “hero.”

A spokesman for the U.S. military assistance mission in Kabul confirmed that the convoy was attacked Wednesday morning near its base at the Kandahar airport. He said there were casualties but did not provide details.

NATO soldiers secure the scene of a suicide bomb attack that targeted a NATO convoy in Kandahar, Afghanistan, on Aug. 2. (Muhammad Sadiq/European Pressphoto Agency)

The Pentagon said Wednesday that two Americans were killed in the attack. Officials did not immediately provide further information.

Witnesses reported seeing two military helicopters land near the site of the bombing and take away wounded troops. A local mechanic whose workshop was near the site told the Associated Press that the force of the blast knocked him unconscious. When he revived, he said, he saw a military vehicle on fire and stepped out of his shop but was driven back by a burst of gunfire.

Kandahar Airfield has long been a hub for U.S. and NATO forces in southern Afghanistan. American troops advise the Afghan army’s 205th Corps at a small installation separate from the larger air base, while Special Operations troops operate from a facility near the city of Kandahar.

Nine U.S. troops have been killed by hostile fire in Afghanistan since the start of the year, six of whom were killed supporting operations against the Islamic State’s Afghan offshoot in the eastern part of the country. More than 2,000 U.S. troops have died in Afghanistan since Afghan forces and U.S. airstrikes drove the Taliban from power in 2001.

The Taliban has increased its attacks in recent weeks as a part of its annual spring and summer offensives. In Washington, the Trump administration is weighing whether to send about 4,000 additional forces to Afghanistan, where the NATO troop total is now about 13,500.

Most attacks are aimed at Afghan defense forces. Last week, 40 Afghan soldiers died in a single insurgent attack in Kandahar. 

A quarterly report released Tuesday by the special inspector general for Afghanistan reconstruction said the conflict between the Taliban and the Afghan government remains a stalemate. It said that from Jan. 1 to May 8, the Afghan security forces had suffered more than 6,000 casualties.

Afghan civilians also have been caught in the crossfire. According to a recent U.N. report, civilian deaths in Afghanistan are at their highest levels since the U.N. mission to Afghanistan began tracking them in 2009.

Gibbons-Neff reported from Washington.