KABUL, Afghanistan (AP) — Militants attacked a remote guesthouse and killed nine Afghans working for a Czech charity on Tuesday, as a new report by a U.S. university warned that almost 100,000 people have been killed in Afghanistan since the 2001 U.S.-led invasion.

Tuesday’s attack took place in the Zari district of northern Balkh province at 2 a.m., when gunmen burst into the workers’ rooms as they slept, said Abdul Basset Ayni, director of the province’s rural development department.

Nine people, including a woman, who were working on reconstruction projects were shot dead. They were employed by a Czech organization called People in Need, and included five project staff, two guards and two drivers, the charity’s country director Ross Hollister told The Associated Press.

Hollister said the staff were working on infrastructure projects for the Afghan government’s National Solidarity Program, which oversees rural development projects across the country.

“They were building schools, hospitals, water projects,” Hollister said. People in Need has been in Afghanistan for 12 years, he said, and has projects in all 104 of Zari’s villages.

Afghan President Ashraf Ghani condemned the attack as the work of “terorrists.” The charity said the assault was “unprecedented in its brutality” and announced it was suspending work in Afghanistan.

Mark Bowden, the U.N.’s humanitarian coordinator for Afghanistan said he was appalled by the attack, which “highlights the challenges aid workers face and the unacceptable sacrifices” they make when working in Afghanistan.

All the dead were Afghan nationals, Ayni said, adding that an investigation team had been sent to the area. The motivation and perpetrators were still unknown and no group immediately claimed responsibility for the attack.

Balkh has recently been beset by insurgent activity and a spike in violence since the Taliban launched its warm-weather offensive in late April.

Guesthouses favored by foreigners have been targeted in the capital, Kabul, by Taliban militants in recent weeks. Fourteen people were killed at the Park Palace Hotel in mid-May, including nine foreigners. The Taliban have said that foreign installations are among their priority targets as the 13-year-old war escalates across the country.

A revitalized insurgency appears to be using a new strategy of sending much larger numbers of men on the battlefield to fight and hold territory, and has, according to Afghan officials, linked up with other anti-government and extremist groups, including the Islamic Movement of Uzbekistan and the East Turkestan Independence Movement.

Meanwhile, a study by Brown University warned that almost 100,000 people have been killed following the overthrow the of Taliban regime that sparked an insurgency. The study — called Costs of War and produced by the university’s Watson Institute for International Studies — looked at war-related deaths, injuries and displacement in Afghanistan and Pakistan from 2001 to last year, when international combat troops left Afghanistan.

Along with those killed, it said that another 100,000 people had been wounded in Afghanistan. For both countries, civilian and military deaths total almost 149,000 people killed, with 162,000 seriously wounded, according to the report’s author, Neta Crawford.

Noting a rise in annual figures for those killed and wounded in recent years, she said the figures show the war in Afghanistan is not ending.

“It is getting worse,” Crawford said.

The study is also backed by U.N. figures, which show that in Afghanistan, civilian casualties rose 16 percent in the first four months of 2015, with 974 people killed and a further 1,963 wounded.

While military deaths are logged with precision, Crawford said, civilian figures are difficult to source. The report’s figures are based on statistics from the United Nations Assistance Mission in Afghanistan, as well as other sources, she said.

Most civilian deaths happened after 2007, with more than 17,700 civilian deaths recorded by UNAMA between 2009 and 2014. Most civilians were killed by militants, she said.

Breaking the figures down, the report found that 26,270 Afghan civilians have been killed and 29,900 wounded as a direct consequence of the war.

A downward trend in civilian deaths that began in 2008 had reversed, she said, and last year it became clear that insurgents were not distinguishing between civilian and combatants. Deaths that are impossible to attribute have also begun to rise.

As a consequence, “the health care system remains burdened by war and stressed due to the destruction of infrastructure and the inability to rebuild in some regions,” Crawford said.

An ongoing humanitarian crisis has been exacerbated by attacks on humanitarian workers by militants, she said in the report.

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Associated Press writers Humayoon Barbur and Amir Shah in Kabul contributed to this report.

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