More than a million civilians in Mosul were in grave danger and aid workers were "bracing for the worst", a relief group said Wednesday, after Iraqi forces reached the jihadist-held city.
Gunfire echoed across the village of Gogjali on the edge of Mosul on Wednesday, as elite Iraqi forces nearby continued a push that had brought them to within a few hundred metres of the city's eastern edge.
Just over two weeks into the offensive to retake Mosul -- the last Iraqi city under the control of the Islamic State group -- Iraq's military said on Tuesday its forces had penetrated city limits by entering a southeastern neighbourhood.
There were no signs yet of a major push inside Mosul itself and on other fronts Iraqi forces were still some distance from the city.
But the Norwegian Refugee Council, one of the most active relief groups operating in Iraq, warned that a long-feared humanitarian crisis was closer than ever.
"We are now bracing ourselves for the worst. The lives of 1.2 million civilians are in grave danger, and the future of all of Iraq is now in the balance," NRC Iraq director Wolfgang Gressmann said in a statement.
- 'Terrifying nightmare' -
"People in and around Mosul have lived for almost two and a half years in a relentless, terrifying nightmare. We are now all responsible to put an end to it," Gressmann said.
More than 20,000 people have already fled to government-held areas since the offensive was launched on October 17, according to the International Organization for Migration.
But civilians inside Mosul -- who according to aid group Save The Children include up to 600,000 children -- are trapped behind IS lines and the United Nations has said thousands are being held for possible use as human shields.
In Gogjali, fighters with Iraq's elite Counter-Terrorism Service (CTS) were screening civilians for any remaining members of IS.
One government fighter carried a black IS flag, saying: "We removed it and planted the Iraqi flag instead."
Backed by air and ground support from a US-led coalition, Iraqi federal forces and Kurdish peshmerga fighters are advancing on Mosul from the east, north and south.
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Soldiers pushing down from the north have moved within two kilometres (1.25 miles) of Mosul, military officials say, while forces moving from the south are still some distance from the city.
Paramilitary forces from the Hashed al-Shaabi (Popular Mobilisation), an umbrella organisation dominated by Iran-backed Shiite militia, also launched an assault at the weekend to cut off the jihadists' escape route to Syria to the west of Mosul.
IS is vastly outnumbered in the battle, with an estimated 4,000 to 7,000 jihadist fighters in Mosul and the surrounding area.
- IS radio reveals tactics -
But the jihadists have put up stiff resistance with suicide bombers, mortars and small arms fire as Iraqi forces advance.
On the southern front, where Iraq's elite Rapid Response Division is advancing towards the IS-held town of Hamam al-Alil some 20 kilometres (12 miles) from Mosul, a captured IS radio provided rare insight into how the jihadists operate.
An AFP journalist embedded with Iraqi forces was present on Tuesday as they listened to IS fighters plan tactics over the radio.
"Abu Dhiyab, let the istishhadi with you go," a jihadist who identified himself as Abu al-Layl said over the captured radio, using an Arabic word the jihadists use for suicide bombers.
Abu Dhiyab replied: "I brought the istishhadiyeen and left them behind the dirt berm. As soon as they (Iraqi forces) advance, they will go out to them."
A Rapid Response captain ordered two vehicles to approach the berm to draw the jihadists out, but the suicide bombers were hit by air strikes before that could happen.
After seizing control of large parts of Iraq and neighbouring Syria in mid-2014, IS declared a cross-border "caliphate", imposed its harsh interpretation of Islamic law and committed widespread atrocities.
IS has been losing ground steadily in Iraq since 2015 and the outcome of the Mosul battle is in little doubt, but commanders have warned it could last months.
If the city is retaken, only Raqa in Syria will remain as the last major city under the jihadists' control.