BAGHDAD, Iraq (AP) – A suicide bomber unleashed a blast in a Baghdad fish market Tuesday and two Shiite families were found slain north of the capital as violence across Iraq claimed at least 51 lives.

The U.S. military, meanwhile, announced the deaths of nine soldiers and two Marines in what has been a deadly period for American forces in Iraq. The announcement brought to at least 15 the number of servicemembers killed in fighting since Saturday.

Sunni politicians expressed worries over a new government plan to stop sectarian violence. The plan, announced a day earlier by Prime Minister Nouri al-Maliki, won some praise in parliament Tuesday, but Shiite and Sunni leaders delayed potentially contentious talks to work out its details.

The four-point plan calls for creating neighborhood Shiite-Sunni committees to monitor efforts against sectarian violence. The aim is to overcome the deep mistrust between Sunnis and Shiites.

Many Sunnis remain skeptical that Shiite leaders will allow security forces to crack down more strongly on Shiite militias blamed for killing Sunnis – including some linked to parties in the government.

“I haven’t seen any real desire in the other side. There are militias supported by the government,” said Sunni lawmaker Khalaf al-Alayan.

U.S. Ambassador Zalmay Khalilzad said that under the plan, parties that have militias have agreed to take “responsibility for what their groups or people under them are doing, … committing themselves to ending the sectarian violence.”

Still, “there are forces that are not under their control,” Khalilzad said in an interview with National Public Radio. “But if they implement what they’ve agreed to, there should be a significant decrease in the level of violence in Baghdad.”

Another lawmaker, Izzat Shabandar, from the secular Iraqi Bloc, cautioned “we have to be realistic.”

“Those who signed this blessed agreement have to confess, at least to themselves, they are the basis of the problem and they are part of it,” he said.

Al-Maliki’s government has been under intense pressure to put an end to Shiite-Sunni violence that has killed thousands of people this year and raised fears of civil war. This week, gunmen carried out two mass kidnappings in as many days, abducting 38 people from workplaces in Baghdad – attacks that Sunnis said were carried out by Shiite militias.

Some 400 Sunnis marched Tuesday at the site of one of the kidnappings – a frozen meat factory in Baghdad’s Amil district – demanding the government put a stop to the violence. Some carried banners reading “get police troops out of our area” – reflecting the widespread suspicion that Shiite-led security forces have been infiltrated by militias.

Gunmen took 24 workers from the factory on Sunday and the bodies of seven were later found dumped in the capital. The fate of the others is not known.

The Interior Ministry said the police commander for the Amil district had been discharged and arrested for investigation in the kidnapping – a possible response to Sunni complaints that Shiite-led security forces allow militias to operate freely.

Earlier Tuesday, a suicide bomber detonated a belt rigged with explosives in an outdoor fish market in the primarily Sunni area of Sadiyah in southwestern Baghdad, killing three people and wounding 19, police said.

Hours later, four mortars hit homes in another Sunni district, killing seven people and wounding 25.

The mixed city of Baqouba, 35 miles northeast of Baghdad, saw a string of deadly attacks. Gunmen opened fire on a Shiite family trying to flee the city, killing five of them. Later, the bodies of a woman and two men lay on the street near the family truck, billowing smoke.

In addition, eight people were killed in another shooting in Baqouba, and two others died in a roadside bombing.

Attacks elsewhere in Baghdad and around the country killed 16 other people.

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