A damaged building is seen at the University of Anbar in the western city of Ramadi on July 26, 2015. Reuters

BAGHDAD (Reuters) — Iraq's armed forces stormed the center of Ramadi on Tuesday to try to dislodge Islamic State militants who have held the western city since May, a spokesman for the counter-terrorism units, Sabah al-Numani, said.

The operation to recapture Ramadi, 100 km (60 miles) west of Baghdad, began early last month after a months-long effort to cut off supply lines to the city, whose fall to Islamic State was a major defeat for Iraq's weak central government.

"Our forces are advancing toward the government complex in the center of Ramadi," Numani said. "The fighting is in the neighborhoods around the complex, with support from the air force."Iraqi intelligence estimates the number of Islamic State fighters entrenched in the center of Ramadi, capital of Western Anbar province, at between 250 and 300.

Retaking the city would provide a major psychological boost to Iraqi security forces after Islamic State seized a third of Iraq, a major OPEC oil producer and U.S. ally, last year.