Thousands of American-trained-and-equipped Iraqi ground troops launched a long-awaited large-scale operation Monday against Islamic State militants in Anbar province, U.S. officials said.

On Monday morning, a spokesman for Iraq’s Joint Operations Command, Brig. Gen. Yahya Rasool, said in a televised statement that Iraqi government forces, backed by Shiite and Sunni pro-government fighters, began an assault on Ramadi at dawn.

The role of the U.S. military was initially unclear because Rasool didn’t clarify whether the U.S.-led international coalition was taking part. In the past, the U.S. military has been reluctant to support some Iraqi operations with heavy involvement of Shiite militias. […]