An Iraqi journalist told Aljazeera that four Iraqi National Guard members and two policemen were killed.
The journalist said US troops surrounded the hospital where the injured were being treated.
Nizar al-Hiti, a local doctor, said most of the casualties were policemen who had been queuing to receive their salaries when the bomber struck.
Elsewhere, five Iraqis were killed and four others injured when a car bomb targeting a US military convoy exploded in Samarra city north of Baghdad.
A woman and a child are among the injured, police sources said. There were no casualties among US troops.
Also on Monday, 15 Iraqis, among them women and children, were killed when US forces bombed their house in al-Karma district northeast of Falluja.
The forces bombed the house in response to gunfire targeting their military base, witnesses said.
An exclusive Aljazeera image of
refugees from Falluja
The Iraqi Red Crescent has established a relief centre in Falluja, but continued fighting between US-led forces and the resistance makes it impossible for doctors and nurses to move around and treat the wounded, the international Red Cross said on Monday.
The Red Crescent has found a city still under siege three weeks after forces launched their offensive, said Rana Sidani, spokeswoman of the International Committee of the Red Cross.
"There are many civilians who are still trapped in the city and don't dare to come to the Red Crescent office," Sidani told The Associated Press from the ICRC's Geneva headquarters.
US troops followed two Iraqis to
their home before killing them
About 110 civilians - including some with chronic disease and fever - are now being sheltered there, but the Red Crescent staff still has not seen any wounded people, she said.
The Red Crescent, the first independent relief group to enter Falluja when it took in an initial convoy a week ago, said it found a mostly deserted city and encountered no wounded then.
"Maybe the injured cannot have access to the centre," which was set up late last week, Sidani said.
"And the doctors' and nurses' access inside the city is restricted because of the fighting."
In other violence two members of the same Iraqi family were killed by US fire inside their home in al-Latifiya district south of Baghdad, Aljazeera has learned.
US forces, who suspected the two had detonated an explosive device planted on a road in the area, had followed the two to their home.
US marines said they killed several anti-American fighters, and detained 32 suspects in a series of actions south of Baghdad on Sunday that included a high-speed riverborne raid on suspected weapons dumps on the Euphrates.
Two marines were also killed in the region, known as Babil (Babylon) province. A marine spokesman gave no further details.
About 40 marines and 80 newly trained Iraqi interior ministry commandos, aided by British soldiers, waded ashore after a dawn race upstream to a point on the east bank opposite Camp Dogwood, where Scottish troops of the Black Watch regiment are based.