More than 4,000 volunteers answered the call of a top Shiite cleric in Iraq to step up and help defend the country from Sunni militants.

The volunteers, mostly young men, were taken by helicopter from Baghdad to Ramadi, the capital of the predominantly Sunni province of Anbar, in a two-day operation that ended Saturday.

The militants on Saturday battled with Shiite militiamen for control of a military base 60 miles north of Baghdad.