KABUL, Afghanistan – An American soldier was killed and another wounded by a roadside bomb on Tuesday during an operation in Afghanistan’s southern Helmand province, the U.S. military said.

The military’s public affairs office in Kabul said the attack took place in Lashkar Gah, the provincial capital, and that six Afghan soldiers were wounded.

“We are deeply saddened by this loss, but remain committed to helping our Afghan partners provide a brighter future for themselves and their children,” Gen. John W. Nicholson, commander of U.S. and NATO forces in Afghanistan, was quoted as saying.

The bombing came a day after officials said 100 U.S. troops had been sent to Lashkar Gah to help defend the city, which appears to be at increasing risk of falling to the Taliban.

Afghan officials say the insurgents effectively control around 80 percent of the province.

The U.S. military said the unidentified soldier was killed while “conducting train, advise, assist activities with Afghan counterparts under NATO authorities.”

It marked the second time this year that an American soldier was killed in hostile circumstances in Afghanistan. In January, a U.S. soldier was killed by small arms fire near the Marjah district, also in Helmand. The U.S. and NATO formally ended their combat role in Afghanistan at the end of 2014, shifting to a training, advisory and counterterrorism mission.

Helmand’s annual $3 billion opium crop produces most of the world’s heroin and is used to fund the insurgency. Its population is mainly Pashtun, the ethnic group from which the Taliban derives most of its support. And the province borders Kandahar, where the Taliban’s government was based from 1996 until the U.S.-led invasion in 2001.