Iraqi forces on Friday (September 29th) launched the second phase of the assault on the northern town of al-Hawija, one of the last bastions in the country still held by the "Islamic State of Iraq and Syria" (ISIS).

The operation came after ISIS released what it said was an audio recording of its leader Abu Bakr al-Baghdadi urging resistance, the first such intervention in nearly a year, AFP reported.

Since al-Baghdadi's previous message to his followers last November, the territory the group still holds in the cross-border "caliphate" it proclaimed in 2014 has shrunk to a fraction of its former extent.

"A huge military operation has begun to liberate al-Hawija and its surrounding areas," the operation's commander, Lt. Gen. Abdel Amir Rashid Yarallah, said in a statement.

Iraqi forces launched an offensive to retake the extremist enclave around al-Hawija on September 21st, swiftly taking the town of al-Sharqat on its second day before pushing on towards al-Hawija itself.

Yarallah said that Friday's assault marked the second phase of the operation and aimed to recapture al-Hawija and the towns of al-Abbasi, al-Riyadh and al-Rashad to its west, east and south.

Troops were now advancing on the town of al-Abbasi, he said.

The operation involved the army, the federal police, counterterrorism units and the Rapid Intervention Force, as well as tribal volunteers.

The enclave lies east of the Tigris River and south of one of its major tributaries, the Little Zab, and troops erected pontoon bridges during the night to enable the assault to begin, Yarallah said.

Prime Minister Haider al-Abbadi hailed the second phase of the operation to recapture the area.

"As we promised the sons of our country, we are going to liberate every inch of Iraqi land and crush the ISIS terrorist gangs," he said.

"We are on the verge of a new victory to liberate the residents of these areas from those criminals."

The al-Hawija enclave is one of just two areas of Iraq still held by ISIS, along with a stretch of the Euphrates Valley near the Syrian border which is under attack too.