The last functioning bridge over the River Tigris in Mosul has been put out of service by a US-led coalition air strike, so-called Islamic State says.
The jihadist group's self-styled news agency posted a video appearing to show a collapsed section of the Old Bridge.
A coalition statement said a strike in Mosul on Monday had "disabled a bridge", without providing details.
Meanwhile, Prime Minister Haider al-Abadi has predicted that it will take three months to eliminate IS in Iraq.
Asked to respond to a recent statement by the US general commanding coalition forces in Iraq that it would take two years to clear the jihadist group from Mosul and its Syrian stronghold of Raqqa, Mr Abadi said: "The Americans were very pessimistic.
"They used to talk about a really long period but the remarkable successes achieved by our brave and heroic fighters reduced that. I foresee that in Iraq it will take three months."
Mosul had five bridges shortly before pro-government forces launched a major offensive to recapture the city 10 weeks ago.
Two were damaged in air strikes in October and two others in November, as part of what the coalition said was an effort to impeded the freedom of movement of IS militants.
They were using the bridges to reinforce and resupply their positions in eastern Mosul, where special forces and army units have been making gains.
Despite this, the coalition left the Old Bridge intact until early December, when air strikes reportedly left craters on approach roads on both sides.
Those attacks happened soon after the bridge was shown in an IS propaganda film featuring the British journalist John Cantlie, who has been held hostage by the group since 2012.
In the film, Mr Cantlie said damage to the bridges and other critical infrastructure inside Mosul was having a detrimental impact on the lives of civilians.
The video footage posted by the Amaq news agency on Tuesday seemed to show that a 40m (130ft) section of the Old Bridge near the eastern bank of the Tigris had collapsed completely into the water.
People were also shown using small rowing boats to cross the river.
Some men who were interviewed complained that the coalition was responsible for the hardship inflicted on civilians.
The UN's International Organisation for Migration has warned that the destruction of the bridges could hamper the evacuation of the more than a million civilians inside Mosul as pro-government forces advance further into the city.
More than 115,000 people have been displaced since the offensive began.