BAGHDAD -- A week after the deadliest attack in Iraq in more than two years, a scattering of smaller bomb attacks around the country on Sunday raised fears of a sustained escalation in violence as American forces withdraw.

The bombings, which killed at least 12 people and wounded more than 50, killed both police officers and civilians and struck Sunni as well as Shiite areas.

Though violence in Iraq has fallen sharply since 2007, many Iraqis fear an increase before parliamentary elections scheduled for Jan. 16. Since the attacks on Oct. 25, which killed 155 and destroyed three government buildings in Baghdad, the authorities have arrested dozens of suspects and security officers, and critics have lashed out at the government for failing to provide security.

Vice President Tariq al-Hashimi said in a statement on Sunday that the Baghdad attacks were preventable, and he blamed "catastrophic gaps and breaches in security forces."

Also on Sunday, a special envoy from the United Nations arrived in Baghdad to investigate security here. Iraqi leaders had asked the United Nations Security Council to study the role of neighboring countries in last week's attacks.

Meanwhile, Iraqi legislators again failed to agree on laws governing the January elections, despite warnings that further delay could prevent the vote from taking place on time. Discussions in Parliament on Sunday instead focused on other matters.

In October, 453 Iraqi civilians and security personnel were killed, an increase from a monthly low this year of 379 in September but considerably below the high of 677 in April, according to the Interior Ministry. The statistics do not count deaths in the northern Kurdish region.

In June, United States troops withdrew from cities and towns, handing security responsibilities to Iraqi forces.

In the deadliest of the attacks on Sunday, a bomb on a parked motorcycle exploded near a police patrol and a crowded kebab restaurant near the southern city of Hilla, killing five people and wounding 37.

"No ambulance came at the beginning; that happens all the time," said Habeb Alwan, 25, who said he saw the blast. "Police closed the area of the explosion and people started to fight with them because they wanted to get to the scene to check on their relatives."

Hilla, a predominantly Shiite city about 60 miles south of Baghdad, was the site of a 2005 suicide bomb that killed at least 114 people, then the deadliest single attack since the 2003 invasion.

In Karbala Province, southwest of Baghdad, a magnetic bomb attached to a minibus filled with 21 passengers exploded near a checkpoint, killing three people and wounding 12 others. Karbala, home of one of the most sacred Shiite mosques, had been relatively peaceful until a spate of attacks in the past few months.

Near Ramadi, the southwest point of the Sunni Triangle, a car bomb and a suicide bomber wearing an explosives belt killed two police officers and wounded five people. Ramadi, once one of the most dangerous cities in Iraq, has for two years been a model of progress since tribal leaders and United States counterinsurgency forces defeated a cell of Al Qaeda in Mesopotamia there.

But recent attacks have led to concern that the group and other insurgent forces may be regaining strength. Since September, at least eight attacks on police officers and other officials have killed more than 70 and wounded dozens more in Anbar Province, which includes Ramadi.

Sheik Ali al-Hatem, a leader of the Sunni Awakening, the group credited with helping to bring down the violence, blamed the police and the provincial council for the "deteriorating of the security situation" in the province, saying: "There are no police here. They are just a name with no actions."

Also on Sunday, an improvised bomb in Mosul Province killed two Iraqi soldiers and wounded a third, and four police officers were killed in two shootings there.

In central Mosul, unidentified gunmen stormed an office and killed a lawyer.