More than 30 bombs struck cities and towns across Iraq on Tuesday, killing at least 52 people and wounding about 250, despite a massive security clampdown ahead of next week's Arab League summit in Baghdad.

It was Iraq's bloodiest day in nearly a month, and the scale of the coordinated explosions in more than a dozen cities showed an apparent determination by insurgents to prove that the government cannot keep the country safe ahead of the summit.

Iraq is due to host the meeting for the first time in 20 years and the government is anxious to show it can maintain security following the withdrawal of U.S. troops in December.

"The goal of today's attacks was to present a negative image of the security situation in Iraq," government spokesman Ali al-Dabbagh told Reuters.

"Security efforts will be escalated to counteract terrorist groups' attacks and to fill loopholes used by them to infiltrate security, whether in Baghdad or other provinces."

Tuesday's deadliest incident occurred in the southern Shi'ite Muslim holy city of Kerbala, where twin explosions killed 13 people and wounded 48 during the morning rush hour, according to Jamal Mahdi, a Kerbala health department spokesman.

"The second explosion caused the biggest destruction. I saw body parts, fingers, hands thrown on the road," 23-year-old shop owner Murtadha Ali Kadhim told Reuters.

"The security forces are stupid because they always gather at the site of an explosion and then a second explosion occurs. They become a target."

Blasts also struck in the capital, in Baiji, Baquba, Daquq, Dibis, Dhuluiya, Kirkuk, Mosul, Samarra, Tuz Khurmato, Khalis and Dujail to the north, in Falluja and Ramadi to the west, and Hilla, Latifiya, Mahmudiya and Mussayab to the south. Police defused bombs in Baquba, Falluja and Mosul.

Most of the blasts targeted police checkpoints and patrols.

"This latest spate of attacks is very likely to have been co-ordinated by a large and well-organized group. It is likely an attempt to show the authorities that their security measures are insignificant," said John Drake, a senior risk consultant at AKE Group, which studies security in Iraq for corporate clients.

Army and police forces are frequently targeted in Iraq, where bombings and shootings still occur almost daily.

Al Qaeda's Iraq wing and allied Sunni Muslim insurgent groups say that despite the withdrawal of U.S. forces they will not lay down arms and will continue to battle the Shi'ite-led government.

They have claimed responsibility for nearly all the major attacks so far this year, mounting days of coordinated bombings across the country about once a month since the Americans left.

Although overall violence has declined since the height of sectarian fighting in 2006 and 2007, Iraqis fear their government lacks the wherewithal to impose security nine years after the U.S.-led invasion that overthrew Saddam Hussein.

Tuesday's attacks were the biggest since February 23 when dozens of explosions across the country killed at least 60 people.

A White House spokesman called the attacks "reprehensible acts".

"Despite these efforts by extremists, violence in Iraq remains at near historic lows," he said.

"Iraqi forces have demonstrated their capacity to deal with the security challenges that exist in that country again and again in recent years, and we do have faith in their ability."

EXTRA SECURITY

The Arab League summit on March 27-29 will be the first held in Baghdad since Saddam's invasion of Kuwait in 1990, and Prime Minister Nuri al-Maliki's government considers it the most important diplomatic event yet for post-Saddam Iraq.

Tuesday was also the day after the ninth anniversary of the start of the U.S.-led invasion that toppled Saddam.

Security has been ratcheted up across Baghdad in the run-up to the summit. Since Monday, intensive searches at checkpoints have ground the city of 7 million people to a halt.

In the northern city of Kirkuk, two car bombs exploded near a police headquarters, killing nine people and wounding 42, police and health sources said. In Baghdad, two bombs killed nine people and wounded 28.

Police in the northeastern city of Baquba said they had found and defused nine bombs, including one in a booby-trapped car which was parked on the road with a decapitated body in the driver's seat and the man's head in his lap.

Five other bombs exploded in the town, the capital of Diyala province north of Baghdad, which also saw a smaller string of deadly explosions on Monday night.

By evening, Reuters had recorded 32 separate explosions on Tuesday. The toll of the blasts, as provided by police and medical sources, was at least 52 killed and 249 wounded.

The government says it will be deploying up to 100,000 additional troops and police in Baghdad to impose extra security measures for the summit and will close Baghdad's airport. Hundreds of millions of dollars are being spent on preparations, including renovating hotels, planting trees and paving roads