U.S. intelligence officials said Friday that they believe the Nigerian Islamic group Boko Haram consists of 4,000 to 6,000 "hard-core fighters," as the militants launched attacks on another country in the region.
The intelligence officials said they thought the group was still holding more than 200 schoolgirls whom it captured in April and had dispersed them to multiple locations.
They said that despite Boko Haram's recent claims that it had made overtures to Islamic State militants based in Syria and Iraq, the United States does not think the group is seeking or receiving foreign fighters.
Boko Haram has spent five years waging an insurgency inside Nigeria in an attempt to impose Islamic law on the region, but the militants' attacks have recently increased in frequency and have spread to neighboring countries, including Cameroon and Niger.
On Friday, Boko Haram fighters attacked two towns in Niger but were driven back by forces from Niger and Chad. Niger's defense minister, Karidio Mahamadou, said his forces killed 109 militants during the attacks on the southern towns of Bosso and Diffa. He said four Niger soldiers were killed.
Boko Haram has also attacked towns in Cameroon, including an assault Wednesday on the far northern town of Fotocol that left at least 110 people dead.
The U.S. State Department condemned the attacks Friday "in the strongest terms." State Department spokeswoman Marie Harf said that Boko Haram's "brutality and barbarism know no bounds."
She said the United States was responding to requests from Cameroon, Chad and Niger and was continuing to provide support to governments in the region.
Chad's army stationed several hundred troops in Bosso earlier in the week. The central African country has taken a lead role in the multinational coalition now fighting Boko Haram.
Chadian forces helped Cameroon's army repel Boko Haram militants in Fotocol after two days of intense fighting. Cameroon's defense minister said Thursday that at least 91 civilians, 13 Chadian soldiers and six Cameroonian soldiers were killed, along with an undetermined number of Boko Haram fighters. He said at least 500 people were wounded and warned the final death toll could go higher.
A Fotocol resident, Abou Ismalia, told VOA's French to Africa service that the militants killed everyone inside the town's three largest mosques. Other residents have said the fighters entered the mosques and slit the throats of Muslims who had gathered for early morning prayers.
Boko Haram has killed thousands of people since launching its insurgency in 2009. It has taken over parts of northeastern Nigeria for what it calls an Islamic caliphate. Regional concerns grew when Boko Haram seized a multinational military base on the shores of Lake Chad in January.
Human rights group Amnesty International said the militants also burned down thousands of buildings in the Nigerian town of Baga and areas nearby.
Plans are under way to set up a regional force of 7,500 soldiers to fight the group. Chad, Cameroon, Niger and Benin have pledged to contribute troops.
The insurgency has emerged as a central issue in Nigeria's February 14 presidential election. President Goodluck Jonathan has come under intense criticism for failing to subdue the militants or recover the schoolgirls kidnapped by Boko Haram from the town of Chibok.
The violence has prompted some Nigerians to call for postponing the election. But on Thursday, an advisory council of Nigeria's top leaders said voting should go ahead as planned.