|Peshmerga forces gather in the east of Mosul to attack Islamic State militants in Mosul, Iraq, October 17, 2016.REUTERS/Stringer
Two years after the jihadists seized the city of 1.5 million people and declared a caliphate from there encompassing tracts of Iraq and Syria, a force of some 30,000 Iraqi and Kurdish Peshmerga forces and Sunni tribal fighters began to advance.
Helicopters released flares and explosions could be heard on the city's eastern front, where Reuters watched Kurdish fighters move forward to take outlying villages.
A U.S.-led air campaign has helped push Islamic State from much of the territory it held but 4,000 to 8,000 fighters are thought to remain in Mosul.
The Pentagon said that Iraqi forces were meeting objectives and were ahead of schedule on the first day of the offensive.
Residents contacted by phone dismissed reports on Arabic television channels of an exodus by the jihadists, who have a history of using human shields and have threatened to unleash chemical weapons.
"Daesh are using motorcycles for their patrols to evade air detection, with pillion passengers using binoculars to check out buildings and streets," said Abu Maher, using an Arabic acronym for Islamic State.
He and others contacted were preparing makeshift defenses and had been stockpiling food in anticipation of the assault, which officials say could take weeks or even months. The residents withheld their full names for security reasons and Reuters was not able to verify their accounts independently.
The United States predicted Islamic State would suffer "a lasting defeat" as Iraqi forces mounted their biggest operation in Iraq since the 2003 invasion that toppled Saddam Hussein.
But the offensive, which has assumed considerable importance for U.S. President Barack Obama as his term draws to a close, is fraught with risks.
These include sectarian conflict between Mosul's mainly Sunni population and advancing Shi'ite forces, and the potential for up to a million people to flee Mosul, multiplying a refugee crisis in the region and across Europe.
"We set up a fortified room in the house by putting sandbags to block the only window and we removed everything dangerous or flammable," Abu Maher said. "I spent almost all my money on buying food, baby milk and anything we might need."
The United Nations' humanitarian coordinator for Iraq said the military had told the U.N. it expected the first significant population movement to begin in five to six days, suggesting that is when the assault would move to the city itself.
Lise Grande said Iraqi security forces would transport fleeing civilians, who would be vetted to ensure Islamic State fighters could not hide among them, following residents' reports that militants had shaved off their beards to escape detection.
Video showing rockets and bursts of tracer bullets across the night sky and loud bursts of gunfire was shown on Qatar-based al-Jazeera television after Prime Minister Haider Abadi announced what he called "the heroic operations to free you from the terror and oppression of Daesh".
"We will meet soon on the ground in Mosul to celebrate liberation and your salvation," Abadi said in a speech on state television in the middle of the night, surrounded by commanders of the armed forces.