Iraqi government forces launched a U.S.-backed offensive on Monday to drive IS from the northern city of Mosul, a high-stakes battle to retake the militants' last major stronghold in the country.
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 IS 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 IS.
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 IS 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.
