By Ahmed Rasheed and Patrick Markey
BAGHDAD/ERBIL, Iraq (Reuters) - Iraqi army units surged towards the centre of Mosul on Tuesday in an attack from the city's southeastern edges that could give fresh impetus to the seven-week-old battle for Islamic State's Iraqi stronghold.
Campaign commander Lieutenant General Abdul Ameer Rasheed Yarallah was quoted by Iraqi television as saying troops had entered Salam Hospital, less than a mile (1.5 km) from the Tigris river running through the city centre.
If confirmed, that would mark a significant advance by the Ninth Armoured Division, which had been tied up for more than a month in close-quarter combat with Islamic State on the southeastern fringes of the city.
Residents of Islamic State-controlled districts of east Mosul said by telephone the army had punched deep into the east bank of the city, getting close to the Tigris.
"The fighting right now is very heavy - Iraqi forces have gone past our neighbourhood without entering it. Our area is now practically surrounded by the river and the Iraqi forces," said a resident of the Palestine neighbourhood.
Islamic State's news agency appeared to confirm the advance, saying three car bombers struck the troops near Salam hospital.
A Reuters team saw thick black smoke rising from the area around the hospital. "We made good advances today," said a soldier who identified himself as Abu Ahmed.
Mosul is by far the largest city under Islamic State control and defeat there would roll back the self-styled caliphate it declared in 2014 after seizing large parts of Iraq and Syria.
Some 100,000 Iraqi soldiers, security forces, Kurdish peshmerga fighters and mainly Shi'ite paramilitary forces are participating in the Mosul campaign that began on Oct. 17, with air and ground support from a U.S.-led coalition.
A colonel in the armoured division said Tuesday's assault, launched at 6 a.m., aimed to ultimately reach Mosul's Fourth Bridge, the southernmost of five bridges spanning the river.
The bridge, like three others, has been hit by U.S.-led air strikes to prevent Islamic State sending reinforcements and suicide car bombs across the city to the eastern front.
The last and oldest bridge, built in the 1930s, was targeted on Monday night, two residents said. The structure was not destroyed, but the air strikes made two large craters in the approach roads on both sides.
"I saw Daesh (Islamic State) using bulldozers to fill the craters with sand and by midday vehicles managed to cross the bridge normally. I drove my car to the other side of the bridge and saw also Daesh vehicles crossing," a taxi driver told Reuters.
The army says it is facing the toughest urban warfare imaginable - hundreds of suicide car bomb attacks, mortar barrages, sniper fire and ambushes launched from a network of tunnels. More than a million civilians are still in the city.
The colonel said Tuesday's offensive aimed to overwhelm the militants, who have put up stiff resistance but are hugely outnumbered by the attacking forces.
"We are using a new tactic - increasing the numbers of advancing forces and also attacking from multiple fronts to take the initiative and prevent Daesh fighters from organising any counter-attacks," the colonel said by telephone.
He said the four armoured division regiments, whose tanks and heavy armour have struggled to adapt to street-by-street fighting, had been reinforced by an infantry regiment.
They were aiming for the Wahda neighbourhood, a sprawling southeastern district. Wahda could serve as a launchpad for an advance to the Fourth Bridge, he said.
The Sunni Muslim jihadists, who seized Mosul in mid-2014, are believed to be dug in across the city, but a U.S. general in the coalition supporting Iraqi forces told Reuters they appeared to have committed additional defences to the fight in the east.
The west of the city is more densely populated than the east and has a greater concentration of Sunni Muslims.
"The quality of the enemy we are facing now is markedly declined from a month ago," said Brigadier General Scott Efflandt, a coalition deputy commander.
"What they were saving for the west side of the river they are now committing to the east."
He said the number of militants in the city had probably fallen to around 3,000, from around 3,000-5,000 at the start of the campaign.
Iraqi officials have not given any casualty figures for their own forces. Last week the United Nations said nearly 2,000 members of Iraq's security forces had been killed in November - a figure Baghdad says was based on unverified reports - and that more than 900 police and civilians had also been killed.
(Additional reporting by Ali Abdelatti in Cairo; Writing by Dominic Evans; Editing by Andrew Roche)