BAGHDAD - Iraqi forces broke into Ramadi's city center on Tuesday, pushing closer to its main government buildings in what commanders hope will be a final push to recapture the key provincial capital from Islamic State militants.

Iraqi forces erected a temporary bridge over a canal that separated their soldiers from downtown Ramadi, about 80 miles west of Baghdad, and used it to launch a morning offensive, military leaders said. By nightfall, Iraqi troops were within half a mile of the city's government compound, they added.

Ramadi represents a key battle for Iraqi forces. The capital of Anbar province, it is the largest population center they have tried to retake from the Islamic State.

Backed by U.S. air power, the offensive also marks the Iraqi armed forces' first major battle from which Shiite militias have been largely excluded, testing whether the military can go it alone.

"We've entered the center," said Brig. Gen. Hamid al-Fatlawi, commander of the Iraqi army's 8th Division. Iraqi forces have encountered "simple" resistance from the militants, he said.

Intercepted Islamic State communications in recent weeks had shown that the militants were increasingly desperate, with leaders imploring their fighters to stay and resist. The U.S. military estimates that just a few hundred fighters remain.

Maj. Gen. Ismail Mahlawi, head of the Anbar Operations Command, said Islamic State fighters were acknowledging that they had "lost control" and were fleeing to the Islamic State-controlled town of Hit, 30 miles to the northwest. Mahlawi said he expected victory within 48 hours.

But despite progress on Tuesday, much of the city's center remained in the hands of the extremists.

Iraqi commanders have said they believe they can completely retake the city by the end of the year.

Iraqi forces reported progress on several fronts. Special forces soldiers, who have been leading the fight from the southwest, crossed the Warrar canal using the bridge assembled by military engineers.

All of Ramadi's eight bridges have been destroyed in the fighting. On Monday, Prime Minister Haider al-Abadi thanked military engineers for completing the temporary bridge that allowed troops to cross into the city.

The recapture of Ramadi would represent the latest in a string of defeats for the militants and provide a much-needed confidence boost for Iraq's military.

The presence of civilians has complicated air support, although estimates have varied widely on how many remain. Fatlawi said Iraqi forces have yet to find any civilians in the neighborhoods they have entered.