DAKAR, Senegal — An Islamic State group offshoot is claiming it carried out the attack in Niger that killed four U.S. soldiers and four Nigerien troops in October 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 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.

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