But the Iraqi-led coalition that began the long-awaited offensive on Monday has faced fierce resistance by ISIS in some areas.

Lt Gen Qassim al-Maliki, commander of the Iraqi 9th armored division, told CNN that in the past 48 hours:

  • The armored division has advanced; it is now three to four miles from the outskirts of Mosul
  • Three brigades have liberated 13 villages to north and northeast of Quwayr
  • At least 50 ISIS militants and two Iraqi soldiers have been killed, and 25 soldiers are injured
  • Dozens of suicide vehicles and a large number of IEDS have been destroyed

But another Iraqi military official, speaking on condition of anonymity, told CNN that Iraqi units fighting around the village of Al Absi have been surrounded by ISIS fighters. Al Absi is near Nimrud, 12 miles (20 kilometers) south of Mosul. The area has seen heavy fighting in the last 36 hours.

Edging closer

"Today we've liberated the village of Kani Harami after intense fighting and inflict big losses in Daesh ranks," he said, using an Arabic acronym for ISIS.

"The forces now are dealing with small pockets of Daesh members hiding in makeshift tunnels. Many Daesh militants pulled back to the Abassiya village. My forces captured two Iraqi national Daesh members in Kani Harami."

He said that the division is closing in on Mosul, and is only around three to four miles (five to six kilometers) from the city's outskirts. He added that progress has been slowed by the need to leave protective forces to hold the ground liberated from the jihadists.

He said that in the two days since the operation to liberate Iraq's second-biggest city — currently the last remaining major ISIS stronghold in Iraq — began, two Iraqi soldiers had been killed, and a further 25 wounded.

Al-Maliki's acknowledgment that progress is being impeded reflects comments made earlier by Sirwan Barzani, a Peshmerga military commander, who told CNN that the battle to recapture Mosul from ISIS could take two months.

Barzani said it would likely take two weeks for advancing forces to enter the city. Iraq's leaders have said that only Iraqi government troops and national police officers will be allowed to do so amid fears of sectarian retribution, he said.

A 94,000-member coalition which includes Iraqi security forces, Kurdish Peshmerga allies and thousands of irregulars from various minorities are involved in the operation to free Mosul from more than two years of ISIS rule.

The coalition vastly outnumbers its opponents, but ISIS, which has known the push was coming, has constructed elaborate defenses, including a network of tunnels. Coalition forces will also likely face suicide bombs, car bombs and booby traps.

Up to 5,000 ISIS fighters are in Mosul, a US military official said. ISIS' supporters put the number at 7,000.

Freed from ISIS — but not from fear

A CNN team

encountered about 200 people

, including dozens of children, who had left their homes in the village of Al-Adla, which is about 31 miles (50 kilometers) southeast of Mosul, near the Great Zab River, fearful of an ISIS counterattack. It had earlier been cleared of militant control by the 9th armored division.

Families, clustered behind a sand berm, had been trapped in their village since ISIS occupied it more than two years ago.

US involvement

It appeared US troops were at the back of the first column of Peshmerga to cross into ISIS-held territory at dawn Monday. The troops wore clothes consistent with US military — including one who wore a US flag patch on his arm — and were driving vehicles distinctive to US military.

The United States, which lent advisers and air support, had earmarked about 500 of its nearly 5,000 service members in the country for the mission. Most are working on logistics, although there are also special operations forces among that number.

The United States still believes ISIS may try to use a rudimentary mustard agent as a chemical weapon in the campaign's final stages. There are reports of ISIS setting fires to oil and tire pits to try to use the smoke to obscure their locations from aircraft targeting them.