KABUL (Reuters) - Afghan officials are investigating reports of an air force strike in Herat province late on Monday that authorities said killed at least 13 civilians as well as some Taliban fighters.

Civilian casualties caused by U.S. air strikes in Afghanistan have long been a source of friction been the U.S.-backed government and international forces, but over the past two years, the reformed Afghan air force has been conducting more of its own strikes.

Defence Ministry spokesman Dawlat Waziri said Afghan aircraft had conducted a strike on a Taliban target in the western province and had killed 18 insurgents and said officials were investigating reports civilians had also been killed.

“There are reports of civilian casualties, so the minister has appointed a team to investigate,” he said.

A spokesman for the NATO-led international support mission in Kabul referred questions to the defense ministry.

“Our understanding [is] that this was an Afghan Air Force strike,” he said in an emailed statement.

Farhad Jilani, a spokesman for the Herat provincial governor, said 13 civilians had been killed and seven wounded in the air strike in Shindand district.

“There was a command and control center of the Taliban where some Taliban had gathered,” he said.

Taliban spokesman Qari Yousuf Ahmadi said a U.S. air strike had killed 35 women, children and elders.

Both the U.S. and Afghan air forces conduct strikes against the Taliban and other insurgent targets and the incident underlined the risks posed as they have stepped up the pace of strikes in recent months.

The government of President Ashraf Ghani and its Western backers have announced a drive to boost the power of the fledgling Afghan air force as part of a four-year strategic plan to strengthen security forces.

The United Nations said in a report last month civilian deaths and injuries from air strikes had spiked 43 percent in the first half of the year, with 95 people killed and 137 wounded.

(Story refiles to fix spelling of Herat in paragraph one.)