WASHINGTON — Opening a new front in the drone wars against Al Qaeda and its affiliates, President Obama announced on Friday that about 100 American troops had been sent to Niger in West Africa to help set up a new base from which unarmed Predator aircraft would conduct surveillance in the region.

The new drone base, located for now in the capital, Niamey, is an indication of the priority Africa has become in American antiterrorism efforts. The United States military has a limited presence in Africa, with only one permanent base, in Djibouti, more than 3,000 miles from Mali, where insurgents had taken over half the country until repelled by a French-led force.

In a letter to Congress, Mr. Obama said about 40 United States military service members arrived in Niger on Wednesday, bringing the total number of those deployed in the country to about 100 people. A military official said the troops were largely Air Force logistics specialists, intelligence analysts and security officers.

Mr. Obama said the troops, who are armed for self-protection, would support the French-led operation that last month drove the Qaeda and affiliated fighters out of a desert refuge the size of Texas in neighboring Mali.