The sounds of automatic rifles firing, rocket-propelled grenades exploding and helicopters buzzing through the sky reverberated through the northern city of Mosul on Thursday, with a ferocity that took some residents back to the early days of the invasion of Iraq.
Halla Mukdad, a professor of economics and business administration at Mosul University, said she could not leave her home.
"The armed people are right outside our house door," she said.
In the spring of last year, it was US armor rolling in. Now, it was insurgents -- storming police stations and stealing guns, ammunition and body armor; setting fire to buildings and police cars; and even making off with a generator.
Later, gun battles with US and Iraqi forces broke out at the five Tigris River bridges the insurgents had seized. Kiowa helicopters swooped above the palm trees and sand-colored buildings, surveying the streets.
Mosul, the third-largest city in Iraq, has been torn by deadly violence throughout the occupation, with car bombings and assassinations becoming almost a routine part of daily life.
But the assaults have grown so incendiary over the last two days that the Stryker Brigade, the light-armored mobile unit charged with controlling the region, is pulling its battalion out of the Fallujah operation to send it north. Three Stryker battalions are already in the Mosul area.
US commanders have said insurgent leaders probably fled from Fallujah in the days or weeks before the offensive there and may be organizing the wave of counterattacks roiling central and northern Iraq. Mosul has seen the toughest fighting outside Fallujah.
In the morning, as the attacks on the police stations began, 13 sedans full of jihadists pulled up to the police academy. They opened fire with rifles and rocket-propelled grenades. When they realized no one was inside, they broke open the doors and began looting.
The same thing happened at the Zuhoor police station, where the generator was carted away.
One group laid siege to the headquarters of the Patriotic Union of Kurdistan, one of the country's main Kurdish political parties. The building once housed the local offices of the Baath Party of Saddam Hussein and was set back from the residential areas. A half-dozen Kurdish militiamen managed to hold off the attackers with heavy machine guns.
The US counteroffensive had begun in an area called the Yarmouk Circle and later spread to other neighborhoods in the south of the city, said Lieutenant Colonel Paul Hastings, a spokesman for the task force that includes the Stryker Brigade. Insurgents melted away whenever the brigade's high-speed vehicles approached, he said.
Hastings said the insurgents had made only limited inroads.
"There are pockets of insurgents," he said. "The city is not falling apart by any stretch of the imagination."
An Iraqi reporter for The New York Times who drove around Mosul on Thursday saw some Stryker vehicles in the suburbs and on the highway to the airport, but few in the city. He encountered no Iraqi policemen, but saw carloads of insurgents brandishing Kalashnikovs and rocket-propelled grenade launchers.
Mosul is a diverse city with large numbers of Sunni Muslims, Christians and Kurds.