An Iraqi paramilitary force says it has seized a key road west of Mosul, effectively encircling the city controlled by so-called Islamic State.
The Popular Mobilisation (Hashd al-Shaabi) declared it had taken control of the road between Tal Afar and Sinjar after linking up with Kurdish forces.
IS militants still control the section of the road between Tal Afar and Mosul.
Meanwhile, an air strike reportedly hit another bridge in Mosul, as troops advanced further into eastern areas.
There is now only one functioning bridge left spanning the River Tigris, which flows through the city.
About 50,000 Iraqi security forces personnel, Kurdish fighters, Sunni Arab tribesmen and Shia militiamen are involved in the five-week-old offensive to drive IS militants out of their last major urban stronghold in the country.
The Popular Mobilisation, which is dominated by Iranian-backed Shia militias, said it had cut the road between the IS-held town of Tal Afar, 50km (31 miles) from Mosul, and Kurdish-controlled town of Sinjar, 45km (28 miles) further west, on Wednesday afternoon.
A Kurdish security official told the AFP news agency that PM fighters had linked up with other anti-IS forces, including members of the Turkish Kurdistan Workers' Party (PKK), in three villages in the area.
A prominent PM leader, Abu Mahdi al-Mohandes, suggested it would now focus on severing the route between Mosul and Tal Afar.
But the PM has been warned by the Turkish government not to attempt to storm the predominantly Sunni Turkmen town, from which thousands of civilians have reportedly been leaving.
Tal Afar official Nuraldin Qablan told Reuters that about 3,000 families had fled the town, with half of them heading south-west towards Syria, and the other half towards Kurdish-held territory in the north.
"We ask Kurdish authorities to open a safe passage for them," he said.
Shia militias have been accused of committing serious violations, including abducting and killing Sunni civilians, during previous operations against IS.
Also on Wednesday, troops continued to advance further into eastern Mosul, where they have faced fierce resistance from the 5,000 to 6,000 militants estimated to be dug in inside the city.
Earlier, the US-led multinational coalition supporting the offensive bombed another of the bridges over the River Tigris that link eastern and western Mosul.
An Iraqi military commander told the Associated Press that the strike on the so-called Third Bridge had taken place before dawn, while a report by IS's self-styled news agency, Amaq, reported that it had been "put out of service".
There were five functioning bridges over the Tigris in Mosul shortly before pro-government forces launched a major offensive to retake the city on 17 October.
A month ago, a US air strike destroyed the Second Bridge, in the city centre. Two weeks later, another strike took out the Fifth Bridge, to the north. On Monday, Amaq reported that the Fourth Bridge, the southernmost, had been damaged.
"This effort impedes Daesh's freedom of movement in Mosul," coalition spokesman Col John Dorrian told Reuters news agency on Tuesday, using a pejorative term for IS based on the acronym of its previous name in Arabic.
"It inhibits their ability to resupply or reinforce their fighters throughout the city."
However, the UN's International Organisation for Migration warned that the destruction of the bridges could hamper the evacuation of the estimated 1.5 million civilians inside Mosul.
The UN says 68,000 people have been displaced in the past five weeks, with 59,000 coming from districts surrounding Mosul and the rest from inside the city.