Iraqi forces press into heart of IS-controlled Tal Afar

Iraqi forces on Tuesday recaptured from the Islamic State (IS) group the first three districts of jihadist bastion Tal Afar as the Pentagon chief visited Baghdad in a show of support.

The United Nations said thousands of civilians had fled Tal Afar in the two days since the start of the broad offensive backed by the US-led coalition fighting IS.

After meeting Iraqi Prime Minister Haider al-Abadi in Baghdad, US Defence Secretary Jim Mattis said the jihadists were "on the run".

"Cities have been liberated, people freed from ISIS, from Daesh," Mattis said, using alternative names for IS.

The militants had not been able "to stand up to our team in combat, and they have not retaken one inch of ground that they lost", he said.

Iraqi troops backed by a US-led international coalition routed IS in Mosul in July after a gruelling nine-month fight for Iraq's second city.

They launched an offensive Sunday to recapture Tal Afar, once a key IS supply hub between Mosul - around 70 kilometres (45 miles) further east - and the Syrian border to the west.

IS fighters inside Tal Afar, estimated to number around 1,000, responded with artillery fire Tuesday as Iraqi forces massed outside the city.

Civilians trapped

More than 30,000 civilians have already fled the conflict, said Lise Grande, a UN humanitarian official in Iraq. Thousands more are expected to flee as the conflict intensifies, with many families making preparations to evacuate.

"Families are trekking for 10 to 20 hours in extreme heat to reach mustering points. They are arriving exhausted and dehydrated," said Grande.

"Food and water are running out, and people lack the basic necessities to survive," she added, highlighting the need to protect civilians trapped in the conflict.

The government is leading the humanitarian operation, providing transport and aid. Humanitarian agencies are helping to cover gaps by providing assistance at mustering points and supporting families when they reach emergency sites and camps.

Security forces launched an offensive to take back the city on Sunday, their latest objective in a US-backed campaign to defeat IS, which remains in control of territory in western Iraq and eastern Syria.

The militants inside Tal Afar - estimated to number about 1,000 - responded with artillery fire as the Iraqi forces massed outside the city.

The UNHCR, the UN refugee agency, has taken control of refugee camps to house those who have fled. Arrangements are being made to open Al-Salamiyah camp in about 10 days, while the Nimrud camp, seven kilometres away, is expected to house up to 22,000 displaced civilians.

About 150 Tal Afar families are sheltered in UNHCR camps east of Mosul.

'IS days are numbered'

The US defence secretary, James Mattis, said on Tuesday that the days of IS were coming to an end in Iraq, as he prepared to travel to Baghdad for talks with Iraqi officials.

"ISIS's days are certainly numbered, but it is not over yet and it is not going to be over any time soon," Mattis said in Jordan.

"Right now our focus is on defeating ISIS inside Iraq, restoring Iraqi sovereignty and territorial integrity."

Iraqi forces had "fought like the dickens in Mosul, (it) cost them over 6,000 wounded, somewhere over 1,200 killed", he noted.

Mattis said Iraqi forces would move against the western Euphrates River valley after retaking Tal Afar.