Kurdish forces in Iraq have taken more ground from the Islamic State of Iraq and the Levant (ISIL) group and are moving closer to the northern city of Mosul.

The Peshmerga, a term used by Kurds to refer to Kurdish fighters, delivered aid to Yazidi refugees on Mount Sinjar on Saturday and expanded a major offensive against ISIL in northwestern Iraq after breaking a months-old siege.

The Peshmerga closed in on Sinjar town south of the mountain and Tal Afar to its east, AFP news agency reported on Sunday.

If successful, the move would significantly alter the map of ISIL's self-declared cross-border "caliphate" and isolate its Mosul hub.

It comes as ISIL reportedly regained control of Beiji city, north of Baghdad. The battle for Beiji and its oil refinery has been running back and forth for months, with each side making gains and suffering losses in the fighting.

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Troops on Sunday retreated to nearby towns surrounding Beiji. ISIL is still in control of the oil refinery, which is about 15 kilometres north of the city.

The autonomous Iraqi Kurdish region's Peshmerga reached the flanks of Mount Sinjar with food and other aid three days after launching a vast operation in the region, backed by US-led coalition air strikes.

As the convoy worked its way up the mountain, a 60-kilometre-long ridge where civilians and fighters had been trapped since September, people swarmed vehicles to receive food.

Tens of thousands of members of the Yazidi religious minority were trapped on the mountain for days in the searing August heat in a first siege that sparked fears of genocide and was one of the reasons that led US President Barack Obama to launch an air campaign against ISIL.

Many were eventually evacuated when a coalition of Kurdish forces opened a corridor to Syria, and on Saturday the same factions were trying to reopen that route.

A statement from the Kurdish president's son, who also heads the Kurdish Regional Security Council (KRSC), said the Peshmerga had cleared villages on the northern side of the mountain.

The Syrian Kurdish YPG group, which has been leading the battle against ISIL in the town of Kobane on the Syrian-Turkish border, was moving south to join up with the Peshmerga.

In addition to opening a safe corridor between Sinjar and the Kurdish areas of Syria, the YPG said on Sunday it had captured seven villages from ISIL on the Syrian-Iraq border - three on the Syrian side and four on the Iraqi side.

The leaders of autonomous Kurdistan described the operation they have spearheaded since Wednesday as the most successful so far against ISIL.

After the US-led coalition paved the way with some 50 air strikes, about 8,000 Peshmerga reclaimed some 700 square kilometres.

Source: Agencies