BAGHDAD — The Iraqi government declared on Monday that it was beginning a major military operation to retake the western province of Anbar from the Islamic State, which occupies much of the area including its major cities, Ramadi and Falluja.

It was not immediately clear if the operation would be more effective than an earlier one that Iraq announced in May, when the Islamic State seized Ramadi, the provincial capital, after holding Falluja for more than a year. Little has changed on the ground since then.

But a barrage of 29 American-led airstrikes near Ramadi on Monday signaled that the United States was strongly backing the operation, a week after President Obama vowed a “long-term campaign” to defeat the Islamic State, also known as ISIS or ISIL.

Maj. Roger Cabiness, a Pentagon spokesman, said the American-led coalition was stepping up airstrikes in Anbar Province to match the increased tempo of Iraqi military operations.