The explosion late Tuesday erupted from inside the house in the capital's Ghazaliya district as officers were about to enter, a local police official said. Six neighboring houses collapsed from the blast and several residents were believed trapped underneath the rubble. Seven policemen were among the 29 dead.
The police official said the attack was "evidently an ambush" and that "massive amounts of explosives" were used. He said the explosion was apparently triggered by remote control.
The U.S. military said in a statement Wednesday that 1,700 to 1,800 pounds of explosives appear to have been used in the attack. It added that American soldiers and Iraqi troops "worked together through the night to pull potential survivors from the rubble."
Insurgents using car bombs, ambushes and assassinations killed a total of at least 54 people in the Iraqi capital and across the volatile Sunni Triangle on Tuesday, including 31 policemen and a deputy provincial governor. A militant group claimed it executed eight Iraqi employees of an American security company.
The string of attacks — including one in which 12 policemen's throats were slit in their station — were the latest by insurgents targeting Iraqis working with the American military or the U.S.-backed government ahead of the Jan. 30 national elections.
Brig. Gen. Jeffery Hammond, assistant commander of the 1st Cavalry Division that controls Baghdad, said attacks by insurgents are expected to escalate further in the run-up to the ballot.
"We anticipate that the enemy will (continue with) attacks, intimidation, assassinations and other messages designed to destroy life in Baghdad," Hammond said, adding that Iraqi security forces will bear the brunt of providing security for the elections and that U.S. troops will back them up only if needed.
In other developments:
Iraqi leaders said the guerrillas — who are mostly Sunni Muslims — are bent on triggering ethnic strife before next month's poll.
"The terrorists intend to destroy Iraq's national unity," a statement issued by the Interim National Assembly said. "Their intentions are to harm this country which faces crucial challenges amid a very difficult period."
Shiite Muslims, who make up around 60 percent of Iraq's people, have been strong supporters of the elections, which they expect to reverse the longtime domination of Iraq's Sunni minority. The insurgency is believed to draw most of its support from Sunnis, who provided much of Saddam Hussein's former Baath Party membership.
Also on Wednesday, a Defense Ministry spokesman in Baghdad confirmed that the Iraqi National Guard — a paramilitary internal security force that has borne the brunt of the anti-insurgency effort — will be merged with the regular armed forces.
The national guard is also part of Iraq's Defense Ministry, and U.S. planners had intended it to be the main security force in the country. Several units took part in U.S.-led campaigns to retake the cities of Samarra and Fallujah from the rebels. But with the war escalating and combat losses mounting, the move is an apparent effort to improve the efficiency of the security forces ahead of elections.
Earlier Tuesday, gunmen attacked a police station near Saddam's hometown of Tikrit, overwhelmed 12 Iraqi policemen there, slit their throats and then blew up the building, said Lt. Col. Saad Hmoud, a local police official.
The deputy governor of the restive Anbar province, Moayyad Hardan al-Issawi, was assassinated near Ramadi, east of Baghdad, police official Abdel Qader al-Kubeisy said.
Gunmen who shot him left a statement next to his body: "This is the fate of everyone who deals with the American troops." The statement was signed by the group Mujahedeen al-Anbar, or "holy warriors of Anbar."
Such flagrant attacks appear designed to cause panic among Iraqi officials and security forces and to provoke a sectarian conflict between Shiites and Sunnis.
Militants released a videotape Tuesday, saying they have executed eight and released two Iraqis who were employed by Sandi Group, an American security company, and had been held hostage since Dec. 13. The claim could not be independently verified.