More than 80 people were killed and dozens were wounded Monday in a string of attacks across Iraq, the deadliest day in the country this year, police and government officials said.

In the worst incident, two bombs exploded in a busy market in the city center of Kut, killing at least 42 people and injuring more than 50.

In an apparently coordinated series of attacks Monday morning, bombings cut a swath from the northern city of Kirkuk to the pricey Mansour district of Baghdad and south to Najaf. Elsewhere, assailants wielding AK-47s targeted anti-terrorism leaders in Diyala province, northeast of Baghdad.

As night fell on the capital, the violence continued. Men wearing Iraqi army uniforms entered a mosque in Yusufiyah, a town near Baghdad, and executed seven men in the middle of their evening prayers during the holy month of Ramadan. The assailants left a note saying the killings were carried out by the Islamic State of Iraq, a Sunni extremist group affiliated with al-Qaeda.

The bloody day came after a period of relative quiet in the country that had descended as Ramadan began early this month.

Lt. Col. Hachem Neama Abbas, an Iraqi army commander in Baghdad, said the military had been bracing for a new round of violence. The attacks, he said, are proof that insurgents still pose a threat to the country’s stability. They also raise questions about the Iraqi government’s ability to maintain security as U.S. troops prepare to leave the country by December.

“This wave of explosions and attacks is evidence that al-Qaeda is still effective,” Abbas said.

Iraq is debating whether to ask a small contingent of U.S. forces to stay past the deadline. U.S. authorities have said that no official request has been made.

A spokesman for the U.S. military in Iraq, Maj. Angela L. Funaro, said that although it was too early to speculate on the groups behind the day’s violence, it was “eerily similar” to a large-scale attack last year during Ramadan. Then, insurgents from al-Qaeda in Iraq targeted checkpoints and Iraqi forces in several cities, killing at least 53.

The worst violence Monday occurred in Kut, a large city southeast of Baghdad. Insurgents detonated a sound bomb in a crowded area near a jewelry store about 8:45 a.m., said Hassan Abdul Zahra al-Wailey, a spokesman for the local police.

Moments later, a car bomb exploded in the same place, killing 42, including 12 children. Some of the children had beenselling bags to those buying produce at the market.

Ali al-Abbudi, 31, a local journalist, happened to be in the market when the blast occurred. He said he was stunned by the “horror of the scene.”

“There were chopped heads or legs, bodies were blown off and scattered around everywhere,” he said.

In Diyala, 13 people, including four Iraqi army officers, were killed in a series of car bombings, explosions and shootings.

In Tikrit, a man dressed in a traffic police uniform blew himself up at the main gate of the city’s counterterrorism facility. In the melee that followed, another bomber detonated explosives, killing and injuring many who had rushed to help. Nine died, including a high-ranking anti-terrorism official.

Elsewhere, three were killed in a series of car bombings in Baghdad, and nine were killed in attacks on government facilities in Najaf and Karbala.

Kirkuk, a city north of Baghdad, experienced three explosions — including a car bomb that killed one person and a explosion near a church that injured four.

Special correspondents Aziz Alwan in Baghdad, Saad Sarhan in Najaf, Uthman al-Mokhtar in Anbar province and Hassan al-Shammari in Diyala province contributed to this report.