MOSUL, Iraq — Breaking a two-week lull in fighting, Iraqi troops backed by the U.S.-led coalition’s airstrikes and artillery pushed deeper into eastern Mosul on Thursday in a multipronged assault against Islamic State militants in the city.

Elite special forces pushed into the Karama and Quds neighborhoods, while army troops and federal police advanced into the nearby Intisar, Salam and Sumor neighborhoods. Columns of dark smoke rose overhead as explosions shook the city and heavy machine gunfire echoed through the streets.

Stiff resistance by the militants, civilians trapped inside their houses and bad weather have slowed advances in the more than two-month-old offensive to recapture Iraq’s second largest city, the extremist group’s last urban bastion in Iraq. It is the biggest Iraqi military operation since the 2003 U.S.-led invasion.

The battle began around 7 a.m. on a bright but chilly December day and continued until shortly before sundown.

The counterterrorism forces, also known as the Golden Brigade, captured about half of the Quds neighborhood by early afternoon.

A statement by the U.S.-led coalition said Thursday’s offensive opened two new fronts in eastern Mosul, increasing pressure on the militants’ “dwindling ability to generate forces, move fighters or resupply.”

It said that, at the request of the Iraqi government, coalition warplanes had “re-struck” two bridges over the Tigris River in Mosul on Tuesday, and a day earlier “disabled” the last bridge crossing in the city.

“The strikes were conducted to reduce enemy freedom of movement, and to further disrupt ISIL’s ability to reinforce, resupply, or use vehicle-borne improvised explosive devices in East Mosul,” said the statement.

Another coalition statement said an airstrike Thursday that targeted a van used by IS fighters in Mosul was later determined to have been located at a hospital’s parking lot, “resulting in possible civilian casualties.”

The coalition, it added, “takes all allegations of civilian casualties seriously and this incident will be fully investigated and the findings released in a timely and transparent manner.” It was not immediately known how many, if any, were hurt by the airstrike.