House Democrats sent a letter to Secretary of Defense Lloyd Austin last week demanding an investigation into the U.S. military’s potential role in the 2017 airstrikes at a Nigerian refugee camp that killed more than 160 civilians.

According to documents obtained by The Intercept, the airstrikes were deemed a “U.S.-Nigerian” operation, despite initial statements by U.S. officials, such as former Defense Secretary Mark Esper, that placed sole responsibility on the Nigerian government.

“Civilians should never be targeted in war,” co-chair of the Protection of Civilians in Conflict Caucus Rep. Sara Jacobs, D-Calif., said regarding the letter. “Unfortunately, that’s exactly what happened in Nigeria in 2017.”

Conducted on Jan. 17 of that year, the airstrikes hit an internally-displaced persons camp in the town of Rann, Nigeria, near the border of Cameroon and Chad. The Nigerian air force stated that extremists with Boko Haram — a terrorist organization that has been previously linked to both Al-Qaeda and the Islamic State — were hiding in the town and among its attached refugee camp.

Satellite imagery of the camp taken the day after the attack — provided by Human Rights Watch — showed “two distinct areas of destruction in densely populated areas on the western side of the town that are consistent with the detonation of multiple air-dropped munitions.” More than 35 structures were destroyed, including those built solely for refugees.

In total, nine aid workers were killed in addition to the 160 civilians, many of whom were children, according to claims made by Human Rights Watch. More than 120 others were wounded.

In the letter to Austin, House representatives requested an investigation be conducted specifically to determine whether U.S. intelligence led to the airstrike and, if so, if measures were taken to limit civilian casualties.

“A document obtained by a FOIA request revealed an investigation ordered by Brig. Gen. Frank Stokes, Deputy Director of U.S. Africa Command, which referred to the strike as an instance of ‘U.S.-Nigerian operations,’” the letter reads.

“A local news outlet supported by the MacArthur Foundation reported that the Nigerian regional military commander, General Lucky Irabor, alleged that the strike was based on ‘intelligence received’ from ‘one of the powerful countries in the west.’”

The caucus goes on to further demand answers into the Defense Department’s knowledge of the operation, the ensuing investigation, and whether accountability was ever taken within the U.S. military chain of command or by its Nigerian allies.

In the Nigerian Air Force’s acknowledgment of the incident, the country’s Defence Spokesperson, John Eneche said that the attack was carried out because operational maps did not mark the area as a humanitarian base.

“Hence, it appeared as a place that could equally be used for enemy activities,” Eneche said.

However, reports from local media sources and HRW show that a Nigerian military base was within a few hundred meters of the encampment. Satellite footage also revealed how visible the camp would have been from the air, raising further questions about the validity of such claims.

As for the investigation conducted by AFRICOM’s former deputy director, the results were never made public. The Intercept report alleges that the FOIA documents prove that Stokes was directed to essentially bypass any real attempts at determining U.S. culpability.

Stokes was reportedly instructed not to focus “on any person or organization which took part in this strike,” the documents show. “You do not have any authority to compel potentially incriminating evidence from any service member, civilian employee of the U.S., contractor personnel supporting U.S. operations, or foreign military personnel,” the mandate reportedly says.

Representatives from AFRICOM and Special Operations Command-Africa did not respond to Military Times’ requests for comment.

U.S. troops have been present in Nigeria for the better part of the last two decades, deploying both in active combat capacities and in advisory roles for regional allies’ fight against Boko Haram.