By Stephen Kalin and John Davison
ERBIL, Iraq/BAGHDAD (Reuters) - Iraqi forces pushed Islamic State fighters back further in Mosul on Tuesday in a renewed effort to seize the northern city and deal a decisive blow to the militant group, though progress was slow in some districts, the army said.
Iraqi forces and their allies have captured villages and towns surrounding Mosul and seized at least two-thirds of its eastern districts, military officials say, reaching the eastern bank of the Tigris river for the first time on Sunday.
The government had initially hoped to retake Mosul by the end of 2016 but three months into the U.S.-backed campaign, the militants control the territory to the west of the Tigris that bisects the city from north to south.
Iraqi Prime Minister Haider al-Abadi said in December it would now take another three months to drive the militants out of Mosul, the largest city under Islamic State control in Iraq or Syria.
Civilians wounded in the fighting streamed into nearby hospitals and Iraqi forces blamed Islamic State for shooting at fleeing residents and shelling populated areas after losing control of them.
United Nations humanitarian spokesman Jens Laerke said nearly 700 people had been taken to hospitals in Kurdish-controlled areas outside Mosul in the last week and more than 817 had required hospital treatment a week earlier.
"Trauma casualties remain extremely high, particularly near frontlines," he told reporters in Geneva.
The World Health Organization (WHO) said about 50 wounded patients a day had come into emergency wards in Erbil over the past two weeks, up from 32 a day previously.
Recapturing Mosul after more than two years of Islamic State rule would probably spell the end of the Iraqi side of the group's self-declared caliphate, which spans Iraq and Syria.
But advances inside Mosul slowed in November and December as troops engaged in tough urban warfare with the jihadists, who are thought to number several thousand in the city.
The militants fought back with suicide car bombs and snipers hidden among the civilian population. They have also recently blown up sections of two bridges crossing the Tigris to try to slow the Iraqi advance, military officials say.
Abadi said on Tuesday the destruction of the bridges would not stop Iraqi forces from "liberating ... the people of Mosul".
Elite forces in the city's east and northeast have advanced faster since the turn of the year thanks to new tactics and better coordination but there was stiff resistance in the southeast of Mosul, military officials said.
Lieutenant Colonel Abbas al-Azawi, a spokesman for the Iraqi army's 16th division, said Iraqi forces entered Hadba on Tuesday, a large northeastern district, though it would likely take more than a day to capture as IS was using suicide bombers.
Iraqi counter-terrorism service (CTS) units encircled the nearby Sukkar district on Monday and sought to recapture the strategic Mosul University area. The United Nations has said Islamic State seized nuclear material used for research there when the militant group overran a third of Iraq in 2014.
The CTS and army units want to capture all the eastern bank of the Tigris so they can launch attacks on western Mosul.
Mosul's five bridges across the Tigris had already been partially damaged by U.S.-led air strikes to slow the militants' movement before Islamic State blew up two of them.
Coalition spokesman U.S. Air Force Colonel John Dorrian told Reuters last week the new damage done by retreating IS fighters was "severe" but would not stop the advance.
"Every day the Iraqi Security Forces go forward and every day the enemy goes backward or underground," he told reporters in Erbil in Iraq's autonomous Kurdish region on Tuesday.
Fighting in neighborhoods in the southeast of Mosul has been tougher, however, as Iraqi forces push toward the river.
"The challenge is that (IS) are hiding among civilian families, that's why our advances are slow and very cautious," Lieutenant Colonel Abdel Amir al-Mohammedawi, a spokesman for the rapid response units of Iraq's federal police, told Reuters.
He said police and army units had fought their way into the Palestine and Sumer districts over the last day but Islamic State fighters were firing at civilians trying to flee.
"The families, when they see Iraqi forces coming, flee from the areas controlled by Daesh (Islamic State) toward the Iraqi forces, holding up white flags, and Daesh bomb them with mortars and Molotov cocktails, and also shoot at them.
"Whenever they withdraw from a district, they shell it at random, and it's heavy shelling," he said.
Dorrian said militant fighters were hiding in mosques, schools and hospitals, using civilians as human shields.
One resident reached by phone in a recently recaptured district of Mosul said shells had continued to fall near his home, forcing him to move his family to another neighborhood.
"In the 10 days since we were liberated, the bombs haven't stopped. Shells fall every day near the house and we've seen civilians killed and wounded several times," he said, without giving his name.
Another resident said he had heard an Islamic State radio broadcast urging fighters to fire at areas were the civilians remained once the Iraqi army had moved in.
The number of people driven out of their homes by fighting spiked around the beginning of the new push by Iraqi forces, but has since returned to previous levels, the U.N.'s Laerke said.
Since the offensive started in October, some 135,000 people have been displaced, he said, adding that a non-governmental organization had opened a field hospital east of Mosul to take the strain off hospitals in Erbil, some 60 km (40 miles) away.
In a sign Baghdad is keen to revive parts of its economy hit by Islamic State's expansion more than two years ago, the oil ministry said this week it might resume exports via a pipeline to Turkey through Nineveh province, where Mosul is located.
Relations with Ankara may have to improve first, however.
Abadi said relations "cannot move forward one step" without the withdrawal of Turkish troops from Bashiqa camp near Mosul.
Turkey's military presence in northern Iraq, where its forces have trained Sunni and Kurdish fighters, has been a point of friction between the two regional powers since well before the Mosul campaign began.
Iraq's oil ministry also invited an Angolan oil company to start work at two oil fields close to Mosul, which Islamic State withdrew from months ago, setting oil wells alight as they left.
(Reporting by Stephen Kalin and Girish Gupta in Erbil; John Davison, Ahmed Rasheed and Saif Hameed in Baghdad,; Stephanie Nebehay in Geneva; writing by John Davison; editing by David Clarke)