By Ahmed Rasheed
BAGHDAD (Reuters) - Iraqi special forces inched their way through districts of east Mosul on Sunday, clearing pockets of Islamic State militants they said were sheltering among civilians and targeting soldiers with waves of car bombs in the world's "toughest urban warfare".
Troops from the elite Counter Terrorism Service (CTS) broke into Mosul on Monday and have taken seven eastern districts, their first foothold in the Islamic State stronghold since the army retreated in disarray from northern Iraq two years ago.
The three-week Mosul campaign has brought together soldiers, security forces, Shi'ite militias and Kurdish fighters, backed by a U.S.-led coalition, to crush the Sunni jihadists's rule in the largest city they have controlled in Iraq and Syria.
Across the border, U.S.-backed Syrian fighters announced on Sunday the start of their own campaign to recapture Islamic State's Syrian bastion of Raqqa.
Simultaneous offensives on Raqqa and Mosul could bring to an end the self-styled caliphate declared by Islamic State leader Abu Bakr al-Baghdadi from the pulpit of a Mosul mosque in 2014.
Baghdadi, however, has told his followers there can be no retreat in a "total war" with their enemies, and the militants in Mosul have been waging a fierce and brutal defense.
They have deployed waves of suicide car bombs, as well as mortar attacks, roadside bombs and sniper fire against the advancing troops, and officers say they have also left behind fighters among residents of districts taken over by the army.
"That's why we are carrying out the toughest urban warfare that any force in the world could undertake," CTS spokesman Sabah al-Numani said.
"Sometimes they climb to the rooftops of houses where civilians are still living and they hold them hostage and open fire on our forces, because they know we will not use air strikes against targets that have civilians."
Militants also targeted the troops with car bombs, sometimes waving white flags as they approached, he said.
Major General Maan al-Sadi, a CTS commander, told state television Islamic State fighters had launched more than 100 car bombs against his forces in the east, which is just one of several fronts in the Mosul offensive.
Late on Friday, a CTS unit came under attack from the rear after advancing into east Mosul, said a colonel in the Ninth Armoured Division which is also taking part in operations there.
Islamic State militants emerged from houses behind them and isolated the convoy, preventing reinforcements from reaching them. Surrounded and low on ammunition, they had to shelter in houses before they finally got out on Saturday.
The Islamic State news agency Amaq released footage on Sunday of captured or destroyed military vehicles, including the burnt wreckage of a Humvee it said was taken in the eastern district of Aden. Fighters shouted "Allahu Akbar (God is Greatest)" and unloaded ammunition and communications equipment.
Amaq also said Islamic State was behind two bomb attacks on Sunday in Tikrit and Samarra, cities to the south of Mosul, which killed 21 people. Officials said the attacks, carried out by suicide bombers driving ambulances packed with explosives, targeted a checkpoint and a car park for Shi'ite pilgrims.
While the army and special forces have been pushing in to Mosul from the east, Kurdish peshmerga fighters are holding territory to the northeast, and mainly Shi'ite militias have sought to seal off the desert routes to Syria to the west.
Security forces have also advanced from the south, entering the last town before Mosul on Saturday and reaching within 4 km (2.5 miles) of Mosul airport on the city's southwest edge, a senior commander said.
The United Nations has warned of a possible exodus of hundreds of thousands of refugees from a city which is still home to up to 1.5 million people. So far 34,000 have been displaced, the International Organization for Migration said.
Many of those still in Mosul feel trapped, including those in districts which the army says it has entered.
"We still can't go out of our houses.... mortars are falling continuously on the quarter," a resident of the Quds neighborhood on the eastern edge of the city told Reuters by telephone.
Although there was no fighting in his own district - for the first time in five days - he said he could hear clashes in the two neighborhoods immediately to the north and south.
In the northern Malayeen district a witness said Islamic State fighters had set fire to a collection of mobile homes, once used by Iraqi security forces, apparently to create a smokescreen against air strikes.
"I can see flames rising up, near the main street," he said. "Daesh (Islamic State) don't let the fire engines get to the fire to extinguish it".
Several witnesses, on both sides of the Tigris River which splits Mosul's eastern and western halves, said they heard burst of celebratory gunfire after the militants claimed falsely they had made sweeping counter-attacks against the army.
"We heard a voice from the mosque - outside prayer time - of a man shouting: 'Allahu Akbar...brave soldiers of the caliphate have regained control of Bartella and Qayyara," said one resident, referring to two forward bases used by Iraqi forces.
"We know they are lying," he said. "The truth is hidden from no one."
(Writing by Dominic Evans; Editing by Mark Trevelyan)