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Three U.S. Army Special Forces soldiers were killed and two were wounded in Niger on Wednesday, in an ambush by suspected Islamic militants operating from Mali, multiple sources with knowledge of the incident told NBC News.

According to the sources, one soldier form Niger was also killed in the attack.

The U.S. military did not confirm the deaths officially, but did acknowledge that a “hostile fire” incident involving U.S. troops had occurred.

“We are working to confirm details of the incident and will have more information as soon as we can confirm facts on the ground,” said a spokesperson for Africa Command, or AFRICOM. The military generally does not confirm nor identify American casualties until it has ensured that the deceased’s family members have been properly notified.

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White House Press Secretary Sarah Huckabee Sanders told reporters Wednesday night that Gen. John Kelly had briefed President Donald Trump on the incident.

The deaths throw a spotlight on one of the many military operations being conducted in Africa as part of a wide-ranging war on a variety of extremist groups, in a swathe of countries stretching across the continent. According to the French radio broadcaster RFI, a joint Nigerien-American patrol was ambushed near the village of Tongo Tongo, approximately 17 miles from the border with Mali.

“U.S. Forces are in Niger to provide training and security assistance to the Nigerien Armed Forces, including support for intelligence, surveillance and reconnaissance (ISR) efforts, in their efforts to target violent extremist organizations in the region,” said U.S. Navy Lt. Cdr. Anthony Falvo, in a statement released to NBC News. “One aspect of that is training, advising and assisting the Nigeriens in order to increase their ability to bring stability and security to their people.”

A senior military official described it as a "partner training mission."

Northern Mali has been the scene of a complex conflict between multiple Islamist militant groups, including Al Qaeda in the Islamic Maghreb (or AQIM), a secular insurgency backed by the Tuareg ethnic minority group, and government forces backed by the West, primarily France.

If the reports about the location of the casualties are correct, it would indicate a coordinated attack undertaken from territory most recently under the control of the Movement for Oneness and Jihad in West Africa, known by its French acronym, MUJAO.

Niger soldiers run through a ravine to sneak up on a target during a training exercise in Samara, Niger, in 2004. Jacob Silberberg / Getty Images file

Although the United States is known to operate a drone base in Niger and also has forces assigned to counter-Boko Haram operations in the east of the country, this is the first known incident in which American forces have been killed in combat with Mali-based militants.

Much of the American military involvement in Africa is conducted by U.S. Army Special Forces — also known as Green Berets — who work with local militaries in an effort to professionalize their forces under programs dubbed “advise and assist” by the Pentagon.