Tensions have been high in the country since the last American troops left in December, with political crises among Iraq's main Shiite, Sunni and Kurdish factions aggravating concerns.

In the deadliest attack on Thursday, at least eight people were killed and 30 were wounded when a bomb in a parked taxi exploded at the entrance of a Baghdad market in the mainly Shiite Muslim district of Washash, the police said.

"There were bodies scattered everywhere," said a police officer, Ahmed Nouri, who was on patrol nearby when the bomb detonated. "Glass and vegetables covered the whole place."

Most of the victims were vendors setting up their produce in the early hours before shoppers arrived, he said.

Violence in Iraq has fallen since the peak of sectarian fighting in 2006 and 2007, but insurgents remain capable of carrying out lethal attacks.

Almost 200 people have been killed so far in June across the country, many in attacks against Shiite pilgrims and shrines.

The worst episode occurred on June 13 when bombers attacked Shiite pilgrims, killing more than 70 people in one of the bloodiest days since American forces withdrew.

In the central Iraqi city of Baquba, at least six people were killed and 51 others were wounded late Thursday when a bomb concealed in a parked car exploded near shops and cafes in a mainly Shiite area, security and medical officials said.

"The rescue teams are still trying to retrieve corpses from underneath the debris," an official in the provincial health directorate said.

Baquba is the capital of Diyala Province, a fertile agricultural area that has long been one of the most volatile regions, inhabited by a mix of Sunnis, Shiites and Kurds.

A separate car bomb attack in Taji, a town 12 miles north of Baghdad, the capital, killed four and wounded 20 early on Thursday, the police said. The bomb in the mainly Sunni town struck a government building, which was severely damaged.

Another roadside bomb targeting a police patrol killed one officer and wounded five in Abu Dsheer, a Shiite area in southern Baghdad, the police said.

Bombers also struck Falluja in the Sunni Muslim province of Anbar, about 30 miles west of Baghdad on Thursday.

A suicide bomber killed two police officers and wounded four others during an attack against a government compound, the police said. They also reported that three more police officers had suffered injuries in a separate attack to the south of the city when a bomb in a parked car blew up.

Opponents of the Iraqi prime minister, Nuri Kamal al-Maliki, accuse him of trying to consolidate power at their expense. Mr. Maliki is fending off efforts by Sunni, Kurdish and some Shiite rivals to organize a vote of no confidence against him.

Mr. Maliki said Wednesday that he would call for early elections if other political parties refused to negotiate to break a deadlock over power-sharing that threatens to inflame sectarian tensions even more.