MOSUL, Iraq -- An airstrike by the U.S.-led coalition on Wednesday "disabled" a fourth bridge across the Tigris River in Mosul, leaving only one intact crossing in the northern Iraqi city and further disrupting the Islamic State group's supply lines.

The IS-run Aamaq news agency and an Iraqi military commander in Mosul reported the pre-dawn airstrike, the second to target a bridge this week. Two other bridges were destroyed by airstrikes last month.

The airstrike was followed by intense fighting in an eastern Mosul neighbourhood where Iraq's special forces are slowly advancing toward the city centre, hampered by suicide car bombings, snipers and concern over the safety of civilians.

The Tigris River runs through the centre of Mosul, and until now most of the fighting has been on the eastern bank. Iraqi forces are expected to use pontoon bridges when they reach the river.

Brig. Gen. Haider Fadhil of the Iraqi special forces told The Associated Press that his men were slowly pushing back IS fighters in the densely populated Zohour neighbourhood, where several suicide car bombs were destroyed by airstrikes before reaching their targets.

Dozens of families fled their homes, as drones buzzed overhead and airstrikes echoed across the city, sending plumes of smoke into the air. Some residents carried their belongings in plastic bags, with one family arriving on a donkey cart.

A man and his four children were helped to a nearby medical station. All five were bleeding from shrapnel wounds after a mortar round struck their home. Dozens more tried to reach the aid station but were held back by troops, who said they had intelligence that IS was sending suicide bombers disguised as civilians.

Iraqi troops later arrived from the front-lines with a man who was bound and hooded. They said they had caught him setting tires on fire to help shield the militants from view. Trembling, the man said he had been forced to aid the extremists.

Mosul, which fell to IS in the summer of 2014, is still home to more than 1 million people. Fearing a mass exodus, authorities have urged residents to stay inside their homes. But the presence of civilians has prevented the U.S.-backed Iraqi forces from using overwhelming force, slowing their advance.

The UN says at least 68,000 people have fled the fighting in Mosul, including 8,300 over the past four days. The majority of the displaced -- 59,200 -- came from districts outside the city.

Elsewhere in Iraq, seven separate attacks in and around the capital, Baghdad, killed at least 14 people and wounded 47, according to police and health officials, who spoke on condition of anonymity because they were not authorized to brief reporters.

Abdul-Zahra reported from Baghdad. Associated Press writers Bassem Mroue in Beirut and Sinan Salaheddin in Baghdad contributed to this report