ISIS leader Abu Bakr al-Baghdadi
ISIS leader Abu Bakr al-Baghdadi Reuters

Iraqi forces on Friday battled jihadists making what looked increasingly like a last stand in Tikrit but the Islamic State (ISIS) group responded by vowing to expand its "caliphate."

Thousands of fighters surrounded a few hundred holdout ISIS terrorists, pounding their positions from the air but treading carefully to avoid the thousands of bombs littering the city center, reports AFP.

Two days after units spearheading Baghdad's biggest anti-ISIS operation yet pushed deep into Tikrit, a police colonel claimed around 50% of the city was now back in government hands.

"We are surrounding the gunmen in the city center. We're advancing slowly due to the great number of IEDs (improvised explosive devices)," he told AFPon condition of anonymity.

"We estimate there are 10,000 IEDs in the city," he said.

Massively outnumbered, the jihadists' defense consists of a network of booby traps, roadside bombs and snipers through which suicide attackers occasionally ram car bombs into enemy targets.

"Six soldiers were killed and 11 wounded in a suicide car bomb this morning in Al-Dyum neighborhood" in western Tikrit, the colonel said. An army major confirmed the death toll.

Tikrit was the hometown of dictator Saddam Hussein, remnants of whose Baath party collaborated with the jihadists when they took over almost a third of the country last June.

Boko Haram "welcomed"

With crucial military backing from neighboring Iran and a 60-nation US-led coalition, Baghdad has rolled back some of the losses.

It started with operations to secure the Shi'ite holy cities of Karbala and Najaf and bolster Baghdad's defenses, then worked its way north, retaking Diyala province earlier this year.

Commanders see the recapture of overwhelmingly Sunni Arab Tikrit as a stepping stone for the reconquest of second city Mosul further north, which once had a population of two million.

ISIS has countered every military loss lately by ramping up its propaganda war with ever more shocking acts, such as getting a child to execute a prisoner on camera or destroying heritage sites.

On Thursday, the group released a recording presented as a speech by spokesman Abu Mohammed al-Adnani which marks the acceptance of a pledge of allegiance by Nigeria's jihadist group Boko Haram.

"We announce to you the good news of the expansion of the caliphate to West Africa," he said.

Expansion is a pillar of ISIS doctrine and the group has recently declared new "provinces" in the Middle East and North Africa, albeit sometimes in places where it has a limited footprint.

Adnani shrugged off recent losses in Iraq and Syria, vowing to enter Rome, blow up the White House, Big Ben and the Eiffel Tower.

Some analysts have argued that months of battlefield setbacks and air strikes were taking a toll on the jihadist group, and that some of its latest moves concealed growing desperation.

Soleimani "cult"

Adnani lashed out at Iran, which he accused of building its own regional empire by meddling in Iraqi affairs and other regional conflicts.

He called Qasem Soleimani, the commander in charge of Tehran's external operations, "the dirty Safavid (a term ISIS uses in a derogatory way to designate Iranians) leader of the battle."

The once invisible Soleimani, who has been in charge of covert operations for Iran for years, has been ubiquitous on Iraq's frontlines and his myth is growing among Shi'ite fighters.

He appeared in a rare phone video released on Thursday, giving life advice in Arabic, apparently to the sons of a prominent Iraqi militia leader.

The footage was interpreted by critics on social media as further evidence Soleimani was behaving like an all-powerful proconsul.

Pictures of a birthday cake to his effigy were circulating among his supporters on social media, as well as a music video produced by the Iran-backed Harakat al-Nujaba Iraqi militia.

The clip features Iraqi Shi'ite fighters training under Soleimani's reassuring gaze and singing his praise.

Soleimani has been seen with Iraq's top commanders since the start of the Tikrit operation and is thought to be playing a key coordinating role.

"That Soleimani has become acceptable can only be explained by the collapse of the Iraqi army last summer," said Kirk Sowell, the publisher of the Inside Iraqi Politics newsletter.

The way Iraq's army disintegrated when ISIS fighters swept in nine months ago has led many Iraqis to give more trust and credit to the paramilitary Shi'ite groups supported by Iran.

"When people feel endangered, they always reach for a savior," Sowell said.