BAGHDAD, Iraq — Insurgents dropped a homemade bomb from a bridge onto a passing U.S. military convoy in Baghdad today, while another military vehicle struck a land mine in the capital. At least seven U.S. troops were injured in those and other attacks throughout the country, the military said.

The U.S.-led provisional authority today announced a $2,500 reward for information leading to the arrest of anyone responsible for the killing of a member of coalition forces or the Iraqi police, part of measures to stem a deepening insurgency that has brought near hourly attacks on U.S. troops.

Two soldiers were injured in the bridge attack, and two others when the military vehicle struck a land mine, said Sgt. Patrick Compton. In Kirkuk, 175 miles north of the capital, assailants fired a rocket-propelled grenade at a military convoy, injuring three servicemen. The patrol returned fire, but there was no word of Iraqi casualties or arrests.

In other violence, witnesses said three Iraqis — including a 13-year-old boy — were killed following a grenade attack on a police station in a Baghdad suburb. Witnesses told Associated Press Television News that those killed when troops returned fire were not among those who attacked the police station.

Late Monday, insurgents fired mortars at a base near Balad, 55 miles north of the capital, the military said. U.S. forces subsequently caught 12 of the suspected attackers. A British soldier was wounded in a sniper attack in Basra, southern Iraq, while on patrol Sunday night, the Defense Ministry said. The soldier was in stable condition at a British army field hospital where he was being treated for gunshot wounds in a leg, the British government said.

Former New York police commissioner Bernard Kerik, who is in charge of security in Iraq, said that U.S. forces and Iraqi police had arrested Sabah Mirza, a former Saddam bodyguard, on June 26. A July 6 raid on Mirza's farm netted plastic explosives, mortars, a machine gun and 10,000 rounds of ammunition.

Despite the worsening guerrilla warfare, the U.S.-led administration called two new city councils to order — one in the southern Shiite city of Najaf and the other in the chaotic capital. The administration also announced an initial economic agenda, including establishment of an independent Iraqi central bank and plans to rid the country of bank notes bearing the image of Saddam Hussein.

In the south, the U.S.-appointed governor of the holy Shiite Muslim city of Karbala resigned today after allegations of financial improprieties, the U.S. military governor said.

Ali Kammouna, 31, had been the governor of Karbala since May. He was the first postwar governor to be approved by Marines, who have been occupying the southern city since late April.

Kammouna was the second governor in the predominantly Shiite south to lose his job in the past two weeks. The governor of Najaf, another Shiite holy city, was arrested and removed from his post after he was charged with corruption and kidnapping.

Meanwhile, two Arabic television stations aired an audiotape purportedly of Saddam Hussein that they claimed to be new. But journalists familiar with the tape said it sounded remarkably similar to another audiotaped message from the ousted dictator that first appeared in May.

The councils — which join other municipal governments with limited powers emerging around Iraq — are expected to act as a proving ground for national leaders, as the United States prepares for an eventual transition to democracy.

Despite increasing attacks against Americans, no extra troops are needed in Iraq now, the war's retiring commander, Gen. Tommy Franks, told ABC's "Good Morning America" in an interview Monday marking his last day in uniform.

In Florida, U.S. Central Command officially changed leaders in a ceremony Monday, with Arabic speaker Gen. John Abizaid taking over for Franks. Abizaid is a Lebanese-American who was one of Frank's two deputies at Central Command.

There now are some 145,000 Americans and 12,000 coalition forces including British, Poles and others in Iraq. Up to 20,000 international soldiers will flow into Iraq to help, beginning later this month and concluding with deployments at the end of September, the Pentagon has said.

In the Iraqi capital Monday, a polyglot city council met for the first time, bringing together a wide range of members — from tribal leaders in headdresses to women in smart business suits. The role of the 37-member advisory body — which has no spending authority — is to advise the U.S.-led administration.

"It's probably the most important day since April 9th, when the coalition came and liberated you from the dictatorship of Saddam Hussein," said L. Paul Bremer, the top U.S. official in Iraq. "Today marks the resumption of the democratic system in Baghdad, which hasn't been here in 30 years."