MOSUL, Iraq -- Iraqi special forces launched a two-pronged assault deeper into Mosul’s urban center on Friday, unleashing the most intense street battles against Islamic State militants since the offensive began nearly three weeks ago.

Smoke rose across eastern neighborhoods of Iraq’s second-largest city as heavy fighting continued after sundown, with explosions and machine gun fire echoing in the streets as mosques called for evening prayer.

More than 3,000 Iraqi troops took part in the assault under heavy U.S.-led coalition air support, but the pace of the fight also slowed as Iraqi forces moved from fighting in more rural areas with few civilians to the tight, narrow streets of Mosul proper. Sniper fire repeatedly stalled the advance, as commanders called in airstrikes or artillery support after coming under fire.

As the operation got underway, columns of armored vehicles wound through the desert, pushing through dirt berms and drawing heavy fire as they closed in on the middle-class Tahrir and Zahara districts. The area was once named after former Iraqi dictator Saddam Hussein.

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Seven suicide attackers in explosives-laden vehicles barreled toward the troops, with two getting through and detonating their charges, Lt. Col. Muhanad al-Timimi told The Associated Press. The others were destroyed, including a bulldozer that was hit by an airstrike from the U.S.-led coalition supporting the offensive.

At least seven special forces troops were killed and an officer and three soldiers were wounded, said an Iraqi military officer who spoke on condition of anonymity because he was not permitted to brief reporters.

“The operation is going well, but it’s slow. These kinds of advances are always slow,” said Iraqi special forces Capt. Malik Hameed, as ISIS fighters could be seen running in the distance to reposition themselves. “If we tried to go any faster we would take even more injuries.”

An Iraqi television journalist traveling in a Humvee was wounded in one of the suicide car bomb attacks.

Earlier, at the eastern approach to the city’s urban center, militants holed up in a building fired a rocket at an Iraqi Abrams tank, disabling it and sending its crew fleeing from the smoking vehicle. The advance in that area then stalled.

The push began as dawn broke with artillery and mortar strikes on the Aden, Tahrir, and Quds districts, just west of the special forces’ footholds in the Gogjali and Karama neighborhoods, al-Timimi said.

On the heels of the special forces advances, the Iraqi army’s ninth division moved into the eastern Intisar neighborhood, said an officer from the unit who spoke on condition of anonymity because he was not authorized to speak to the media.

On Tuesday, Iraqi troops entered the city limits for the first time in more than two years, after a demoralized Iraqi army fled in the face of the Islamic State group’s 2014 blitz across large swaths of territory in Iraq and neighboring Syria.

The operation to retake Mosul is expected to take weeks if not months. Moving from neighborhood to neighborhood in house-to-house battles through dense warrens of booby-trapped buildings is time consuming and Iraq’s military has repeatedly opted for slower operations in an effort to minimize casualties.

Some 1 million civilians still remain in the city, complicating the advance. ISIS militants have driven thousands of residents deeper into the city’s built-up areas to be used as human shields, while hundreds of others have fled toward government-controlled territory and thousands have fled west into Syria.

Just a few miles (kilometers) from Friday’s operation, dozens of cars queued up on the road to camps for displaced Mosul residents.

“We suffered and there was bombing and heavy shelling. We didn’t feel safe,” said Mahmoud Mahdi, who was fleeing the now government-held Gogjali neighborhood. “Everybody is displaced and walking around in this heat. It is exhausting.”

Mosul is the last major ISIS stronghold in Iraq, and expelling the militant group from the city would be a major blow to the survival of its self-declared “caliphate” that stretches into Syria.

Iraqi forces have made uneven progress in closing in on the city since the operation began on Oct. 17. Advances have been slower from the south, with government troops still some 20 miles (35 kilometers) away. Kurdish fighters and Iraqi army units are deployed to the north, while government-sanctioned Shiite militias are sweeping in from the west to try to cut off any ISIS escape route.

As the sun began to set Friday, special forces troops fanned out across the city blocks retaken in the fighting. Guided by intelligence from U.S.-led coalition surveillance of the area, they knocked on the doors of homes where they believed civilians were living.

Moving from street to street, Capt. Hameed and his men found four families and an elderly couple in the sector they were assigned to clear. After sweeping the rooms for weapons, they questioned the male heads of household.

“Who were the ISIS fighters responsible for this neighborhood?” special forces Maj. Ahmed al-Mamouri asked an elderly man.

“They were Arabs, but not Iraqi. Foreign,” the man said pointing to the houses where the fighters lived and worked.

As his children served the Iraqi soldiers tea, the man described where and when he saw the ISIS militants flee and the weapons they had. Al-Mamouri pulled out satellite images of central Mosul and asked the man to identify checkpoints and buildings where he believed the fighters were making explosives.

“This is all to help with our operation moving forward,” al-Mamouri said. “This is almost more important than the clashes.”