BAGHDAD: A U.S.-backed military offensive against Islamic State fighters faltered in its first week as several hundred militants entrenched in the provincial capital of Ramadi withstood punishing air strikes and held off a far-larger force of Iraqi ground troops, senior U.S. and coalition commanders said Saturday.

The push by pro-government forces to retake Ramadi, which fell to the militants in May, includes about 10,000 members of the Iraqi army, federal police and Shiite militias, and Sunni tribal fighters.