U.S.-backed offensive in Iraq gets off to a disappointing start

Iraqi Shiite fighters with the Popular Mobilization Units in Saqlawiya on the outskirts of Fallouja on July 15, 2015. (Ahmad al-Rubaye / AFP/Getty Images)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 airstrikes and held off a far-larger force of Iraqi ground troops, senior U.S. and coalition commanders said Saturday.

The slow going in what officials portray as a major test of efforts to bring Iraq's fractured security forces into a common front against the Sunni Muslim extremists comes as a truck bomb late Friday killed more than 100 people, including…