The United States pledged $60 million on Monday to a new United Nations-backed antiterrorism force from five African countries including Niger, where four American soldiers were killed early this month.

The pledge, announced by Secretary of State Rex W. Tillerson in Washington and Ambassador Nikki R. Haley at the United Nations, came as the United Nations Security Council was meeting about the vast and lawless Sahel region in western and north-central Africa, where the force will operate.

“Defeating terrorism depends on making sure terrorist organizations cannot have safe havens on any continent,” Mr. Tillerson said in a statement announcing the pledge, which will require congressional approval.

“This is a fight we must win, and these funds will play a key role in achieving that mission,” he said.