Kurdish forces say they are making progress in a major offensive they have launched against Islamic State (IS) militants in Sinjar in northern Iraq.
Peshmerga fighters have reportedly taken a strategically important main road near the town that helps connect the IS strongholds of Mosul and Raqqa.
The offensive is supported by US-led coalition air strikes.
Tens of thousands of others became trapped on nearby Mount Sinjar without food or water for days until they were rescued by Syrian Kurdish forces. The risk of genocide was a key factor in the US decision to launch air strikes in Iraq.
Coalition warplanes bombed IS positions, command-and-control facilities and weapons stores in the Sinjar area overnight before some 7,500 Peshmerga fighters launched a ground assault around dawn on Thursday, closing in on three fronts.
Within hours, they had successfully blocked Highway 47, the main road between Mosul, to the east, and Raqqa to the west, and secured three surrounding villages.
A Peshmerga source later told the BBC's Ahmed Maher that they had managed to seize a key checkpoint on the road at Umm al-Shababit, 26km (15 miles) west of Sinjar, and asserted their control over three hills to the north-west.
The Peshmerga are also laying siege to the 80% of the town of Sinjar that they failed to retake in an offensive in December, when IS was driven from Mount Sinjar.
At the scene: Jim Muir, BBC News, on Mount Sinjar
The offensive by Kurdish forces began in earnest at dawn, with a series of coalition air strikes sending up plumes of smoke around the town of Sinjar.
It lies at the foot of a rugged mountain of the same name, and is strategically placed near the border with Syria.
Peshmerga forces began opening up with rocket fire, and their troops started moving down to join an advance on the ground.
Kurdish forces have controlled part of the town since an attack months ago. But IS militants put up strong resistance, leading to a prolonged stalemate.
The Kurds are clearly determined to win Sinjar back. They are calling this Operation Free Sinjar and say they are throwing 7,500 fighters into the battle.
Sinjar is one of the biggest towns they lost last year, though it was its mainly Yazidi population who suffered the most.
The Kurds are hoping for a swift victory. But advancing against IS in built-up terrain has proved slow and dangerous in the past.
The militants are adept at planting booby-traps and other bombs, often causing heavy casualties.
"We are advancing but carefully and slowly towards the heart of the town because of Daesh booby-traps, snipers, minefields and suicide bombers," the source said, using a pejorative term for IS based on an Arabic acronym of its former name.
A coalition statement said the Sinjar offensive would "degrade Daesh resupply efforts, disrupt funding to the terrorist group's operations, stem the flow of Daesh fighters into Iraq, and further isolate Mosul from Raqqa."
"Coalition air strikes will continue to target Daesh leaders, revenue sources, supply routes, command facilities, and weapons caches to dismantle their operations in Iraq and Syria," it added.
US military advisers were with Kurdish commanders near Mount Sinjar, but were positioned well back from the frontline, a US military spokesman told the Reuters news agency.
The Kurds estimated that there were almost 600 IS militants in Sinjar before the offensive began, but the coalition said they believed some 60 to 70 had been killed in Thursday's air strikes.
Thousands of Yazidis who fled the Sinjar area when it fell to IS in August 2014 are reportedly taking part in the offensive. Turkish Kurdistan Workers' Party (PKK) rebels have trained a Yazidi militia, while others have joined the Peshmerga.
Hussein Derbo, the head of a Peshmerga battalion made up of 440 Yazidis, told the Reuters news agency: "It is our land and our honour. They [IS] stole our dignity. We want to get it back."
Sinjar - a strategic town
- Situated in northern Iraq at the foot of Mount Sinjar, about 30 miles (50km) from the Syrian border
- Highway 47, one of IS's most active supply lines, runs through the town
- Area mainly inhabited by Kurdish-speaking Yazidis with Arab and Assyrian minorities
- Islamic State militants attacked in August 2014
- Some 50,000 Yazidis fled the town and became trapped on Mount Sinjar without food or water
- Since then, Kurdish forces have won back areas of the town but IS resistance has led to a stalemate
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