raqi security forces fire their weapons during clashes with Islamic State militants on the outskirts of Ramadi on June 15, 2015.

Iraqi ground forces stormed Ramadi on Tuesday in an attempt to wrest control of the Iraqi city from the Islamic State, which has controlled it for months.

The troops began their offensive Monday night on the edges of the city, and by midday Tuesday had advanced to its center, according to news reports from journalists on the ground.

The offensive was backed by airstrikes from the U.S-led coalition fighting the Islamic State. The troops numbered up to 10,000 men, and included Iraqi government troops and U.S.-trained counterterrorism forces, according to The Wall Street Journal, as well as Sunni tribal fighters, according to The New York Times.

A spokesman for the U.S.-led coalition, Colonel Steve Warren, told the Journal that U.S. intelligence estimates that only about 250 to 350 Islamic State fighters remain in Ramadi, down from about 600 to 1,000 fighters. Officials told news organizations that they believe Iraqi troops could clear out Islamic State militants and take control of the city in a matter of hours.

The Islamic State, which controls about one-third of Iraq and parts of Syria, seized Ramadi from Iraqi forces in May. The government in Baghdad has launched several ultimately unsuccessful offensives to retake the city since July. But earlier this month, Iraqi forces retook Tamim, a large neighborhood on the southwestern outskirts of Ramadi, as well as a key Islamic State operations center there.