FILE - These images provided by the U.S. Army show, from left, Staff Sgt. Bryan C. Black, 35, of Puyallup, Wash.; Staff Sgt. Jeremiah W. Johnson, 39, of Springboro, Ohio; Sgt. La David Johnson of Miami Gardens, Fla.; and Staff Sgt. Dustin M. Wright, 29, of Lyons, Ga. All four were killed in Niger, when a joint patrol of American and Niger forces was ambushed on Oct. 4, 2017, by militants believed linked to the Islamic State group. The Mauritanian Nouakchott News Agency reported Friday, Jan. 12, 2018 that Abu al-Walid al-Sahrawi with the self-professed IS affiliate claimed responsibility for the Oct. 4 ambush about 120 miles (200 kilometers) north of Niger's capital, Niamey. (U.S. Army via AP)

FILE - These images provided by the U.S. Army show, from left, Staff Sgt. Bryan C. Black, 35, of Puyallup, Wash.; Staff Sgt. Jeremiah W. Johnson, 39, of Springboro, Ohio; Sgt. La David Johnson of Miami Gardens, Fla.; and Staff Sgt. Dustin M. Wright, 29, of Lyons, Ga. All four were killed in Niger, when a joint patrol of American and Niger forces was ambushed on Oct. 4, 2017, by militants believed linked to the Islamic State group. The Mauritanian Nouakchott News Agency reported Friday, Jan. 12, 2018 that Abu al-Walid al-Sahrawi with the self-professed IS affiliate claimed responsibility for the Oct. 4 ambush about 120 miles (200 kilometers) north of Niger's capital, Niamey. (U.S. Army via AP)

DAKAR, Senegal (AP) — An Islamic State group offshoot is claiming it carried out the October attack in Niger that killed four U.S. soldiers and four Nigerien troops and sparked questions about U.S. military involvement in West Africa’s vast Sahel region.

The Mauritanian Nouakchott News Agency reported Friday that Abu al-Walid al-Sahrawi with the self-professed IS affiliate claimed responsibility for the Oct. 4 ambush about 120 miles (200 kilometers) north of Niger’s capital, Niamey. The news agency has carried messages from the affiliate before, according to the SITE Intelligence Group, which monitors jihadist websites.

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The U.S. Africa Command has been investigating the attack, which also wounded two U.S. and eight Nigerien troops. A final report is expected to be released this month.

A 12-member Army special forces unit was accompanying 30 Nigerien forces when they were attacked in a densely wooded area by as many as 50 militants traveling by vehicle and carrying small arms and rocket-propelled grenade launchers.

The Pentagon has declined to release details about the commando team’s exact mission. U.S. officials have said the joint U.S.-Niger patrol had been asked to assist a second American commando team hunting for a senior Islamic State group member. The team had been asked to go to a location where the insurgent had last been seen.

After completing that mission, the troops stopped in a village to get food and water, then left. The U.S. military believes someone in the village may have tipped off the attackers.

The U.S. has approximately 800 troops in Niger, and U.S. special operations forces have been working with Niger’s forces in a growing effort in recent years, helping them to improve their abilities to fight extremists.

Multiple military efforts exist against extremist groups, including Boko Haram and al-Qaida affiliates, that roam the vast Sahel, the sprawling, largely barren zone south of the Sahara desert. The growing fight includes France’s largest overseas military operation, a United Nations peacekeeping mission in Mali and a five-nation regional force called the G5 Sahel that launched last year.

Officials have pointed out the danger and difficulty of hunting down an enemy in region the size of Europe.

The Mauritanian news agency also reported that the extremists claimed responsibility for an attack Thursday on a French military convoy, and for a series of attacks in Niger and border areas with Mali and Burkina Faso.