Strong explosions shook central Baghdad at dawn and heavy fighting erupted in a street notorious as a rebel stronghold, in violence that killed at least 22 Iraqis, the US army and witnesses said.
The clashes flared as the US military pressed on with new offensives aimed at retaking control of guerrilla-held areas ahead of national elections due to be held in January.
In one of the heaviest barrages in the capital for months, insurgents fired more than a dozen mortars or rockets around the Green Zone compound housing the US and other embassies and Iraq's interim government. Black smoke billowed into the sky.
The US military said some rounds landed inside the Green Zone, but there were no reports of casualties.
In other attacks, a car bomb killed a senior police officer, another policeman and a 12-year-old boy on a highway in western Baghdad. A second suspected suicide car bomber tried to force his way through the gates of Abu Ghraib prison but was shot dead by US troops, the military said.
Three people were wounded and explosives were found in the car. Officials had earlier said the car had exploded.