A wave of car bombings rocked central and northern Iraq on Monday, killing at least 57 people and extending the deadliest eruption of violence to hit the country in years.

Attackers initially targeted market-goers early in the morning, then turned their sights on police and army posts after sunset. Security forces scrambled to contain the violence, blocking a key road in central Iraq and imposing a curfew in the former Sunni insurgent stronghold of Mosul after the blasts went off.

Killing in Iraq has spiked to levels not seen since 2008. The surge in bloodshed, which follows months of protests by the country's Sunni Arab minority against the Shiite-led government, is raising fears that Iraq is heading for another bout of uncontrollable sectarian violence.

The upsurge comes as foreign fighters are increasingly pouring into neighboring Syria, where a grueling civil war has taken on sectarian overtones similar to those that pushed Iraq to the brink of its own civil war in 2006 and 2007.

Syria's conflict is fueling sectarian tensions inside Iraq, with Iraqi al-Qaida-linked Sunni militants cooperating with ideological allies among the Syrian rebels, while Iraqi Shiite militants increasingly fight alongside forces loyal to Syria's Iranian-backed regime.

There was no immediate claim of responsibility for Monday's attacks _ as has been the case for much of the violence in recent weeks _ but coordinated car bombings in civilian areas and against security forces are frequently the work of al-Qaida's front group in Iraq, known as the Islamic State of Iraq. 

Monday's deadliest single attack hit Diyala province when three parked car bombs exploded virtually simultaneously around a wholesale fruit and vegetable market at the height of business in the town of Jidaidat al-Shatt. The town is just outside the provincial capital of Baqouba, about 60 kilometers northeast of Baghdad.

The blasts killed 15 people and wounded 46. Soon after the explosions, security forces sealed the roads linking Baqouba to Baghdad in an apparent effort to prevent further attacks.

Shortly after midday, another car bomb went off near a fish market in the northern Baghdad suburb of Taji, killing seven shoppers and wounding 25, police said.

In the northern city of Tuz Khormato, police said a parked car bomb exploded near a small outdoor market just before the sunset, killing three people and wounding 22. The town is about 200 kilometers north of Baghdad.

Baqouba and the surrounding Diyala province were once the site of some of the fiercest fighting between U.S. forces and insurgents in Iraq, and it remains a hotbed for terrorist attacks. The area is religiously mixed and witnessed some of the worst atrocities as Shiite militias battled Sunni insurgents for control in the years after the 2003 U.S.-led invasion.

The three car bombs used in the attack near Baqouba were deployed in different locations in and around the market in order to inflict the most damage and casualties, police said. One of the vehicles was a pickup truck loaded with produce that was parked inside the market. 

Last Friday, Diyala was the site of another deadly bombing. A suicide attacker drove an explosives-laden car into a bus carrying Iranian Shiite pilgrims visiting holy shrines in Iraq, killing 11 and wounding more than two dozen. The attack took place in the town of Muqdadiyah, about 90 kilometers (60 miles) north of Baghdad.

Provincial councilman Sadiq al-Husseini blamed that attack and Monday's bombing in the produce market on al-Qaida-linked groups.

“When the grip is tightened on these groups, they resort to random attacks on residents and foreign pilgrims in order to show to the people that they are still active,” he said. “Our security forces still lack intelligence and bomb detecting equipment” to stop such attacks, he said.

In the evening, a rapid-fire wave of five car bombings erupted in the volatile northern city of Mosul, killing at least 24 and wounding 114, according to Ninevah provincial governor, Atheel al-Nujaifi.

Al-Nujaifi said four of the car bombs exploded when their drivers rammed them into security checkpoints. The fifth detonated while a bomb disposal team was trying to diffuse it.

Mosul authorities imposed a curfew on the city following the blasts. Mosul, the capital of Ninevah province, which borders Syria, has been one of the hardest areas to tame since bloodshed erupted after the U.S.-led invasion that ousted Saddam Hussein.

A suicide car bomber also struck a security checkpoint near Madain, about 20 kilometers southeast of Baghdad, killing four soldiers and wounding 10 others, according to police.

Four others were killed when a bomb exploded near a cafe in the Shiite neighborhood of Sadr City in Baghdad late Monday. Police said the blast injured 12. Another explosion in the al-Ameen neighborhood in southeastern Baghdad wounded six.

Hospital officials confirmed the death tolls. All officials spoke on condition of anonymity because they weren't authorized to release the details to reporters.

According to the United Nations, at least 1,045 Iraqi civilians and security personnel were killed in May. The tally surpassed April's 712 killed _ at the time, Iraq's deadliest month since 2008. According to an Associated Press count, more than 100 people have been killed so far in June. (AP)