And just like Mosul, they left behind their U.S. weaponry for ISIS.

IRBIL, IRAQ — Iraqi security forces attempting to retake control of the western city of Ramadi were routed in heavy fighting Sunday, the worst defeat for Iraq’s central government since Islamic State militants stormed across the country last June.

In a replay of last year’s military debacle, elite units abandoned their U.S.-provided equipment to Islamic State fighters and fled the area, leaving several hundred soldiers surrounded in the last government-held enclave in the city.

Multiple security sources, none of whom agreed to be identified, speaking from both within the besieged Anbar Operations Center as well as with the units fleeing the city, described the fight for control of the capital of Iraq’s largest province as essentially over after reinforcements sent on Saturday to retake the city were crushed by Islamic State fighters.

“Only God can save us,” said one officer speaking by phone from inside the Anbar operations center, where officers had been coordinating the operation. The officer said that several hundred policemen and soldiers were surrounded inside the command center, which was repeatedly struck by suicide bombers and heavy artillery fire as militants cut off their last routes of escape.

Social media accounts credibly associated with the Islamic State announced hours later that the operations center had been overrun, a claim that could not be immediately confirmed. Efforts to reach sources inside the facility were unsuccessful.

The units that had been attempting to retake Ramadi, which was attacked late Thursday evening and had fallen mostly into militant hands by Saturday, were in the process of fleeing the city and had abandoned dozens of U.S.-supplied armored vehicles, as well as artillery, heavy machine guns and other military gear as they fled mostly on foot from the fighting.

The elite Golden Brigade, Iraq’s premier special forces unit, which had withdrawn to the “Stadium” neighborhood south of the city on Friday to await reinforcements and prepare a counterattack had also abandoned its positions and was retreating from the area under heavy attack by Islamic State forces, according to two officers within the unit reached by phone Sunday.

“Ramadi has fallen to Daash,” one officer said. “There were many suicide bombers and many soldiers and officers are dead.” […]

How effective Shiite militiamen deployed far from their home areas in an overtly hostile environment would be remained an open question. The militia played the leading role in the government’s effort to recapture Tikrit two months ago. But the militias took heavy casualties in the predominantly Sunni area and were unable to take the city despite overwhelming numbers. Tikrit fell only after the militias withdrew, and the United States launched air strikes against the Islamic State positions to back regular Iraqi army ground forces.

Those forces, however, were the very ones that fled Ramadi on Sunday.

The capture of Ramadi, a city whose population is given as between 500,000 and 900,000, is by far the largest Islamic State victory since the militants’ June 10 capture of Mosul, which with 2 million people is Iraq’s second biggest city. It comes after nine months of U.S. bombing in Iraq and offers a counter to American military officials’ arguments as recently as last week that those strikes have put the militants on the defensive.