BAGHDAD (Reuters) - A suicide bomber killed eight people in the Iraqi parliament on Thursday, brazenly penetrating to the heart of Baghdad’s Green Zone to launch the deadliest strike yet in the heavily fortified compound.

Defying a two-month-old U.S.-Iraqi security crackdown, the bomber slipped through multiple armed checkpoints to reach the heart of the zone, a 10 sq km (4 sq miles) area housing parliament, government offices and many embassies.

U.S. military spokesman Major-General William Caldwell said initial reports showed eight had been killed and 20 wounded in the blast which tore through a cafe where lawmakers were having lunch. State television said three of the dead were lawmakers.

Caldwell said the blast bore the hallmarks of Sunni Islamist al Qaeda, resurgent in recent weeks despite the crackdown by tens of thousands of Iraqi and U.S. troops.

Footage of the blast broadcast on Iraq’s al-Hurra television station showed a Shi’ite MP being interviewed when suddenly a loud blast sent him ducking for cover. Clouds of dust and debris swirled through the building as people shouted and tried to make their way out down stairwells.

U.S. President George W. Bush and Iraqi Prime Minister Nuri al-Maliki, who is on a trip to the Far East, condemned the attack on the parliament, housed in a former conference centre.

“It reminds us though that there is an enemy willing to bomb innocent people in a symbol of democracy,” Bush said.

A truck bomb also killed at least seven people on Sarafiya bridge in northern Baghdad, a main artery linking east and west Baghdad, destroying most of the steel structure and sending several cars plunging into the River Tigris below.

How explosives were smuggled into the Green Zone is likely to be the focus of an investigation. They would have had to pass through an outer checkpoint manned by U.S. and Iraqi troops and multiple inner checkpoints guarded by security contractors and foreign troops that are part of the U.S.-led coalition.

Iraqi military spokesman Brigadier General Qassim Moussawi, said it appeared to have been a well-planned operation that had taken advantage of “a deficiency in one of the security points”. A review of procedures would need to be carried out, he said.

WHO HAD ACCESS?

Entry to the conference centre is restricted to accredited parliamentary staff, deputies, security guards and journalists. Only MPs, police and kitchen staff can access the cafeteria.

Two Shi’ite lawmakers said the metal detector used at the VIP entrance was working, but a Sunni legislator said when he arrived there was a power cut and bags were being manually searched. A Reuters cameraman said the scanner at a second entrance used by staff and journalists was operating.

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“We are trying to backtrack all the systems to see how somebody was able to get a suicide vest in ... we are looking at who had access there,” Caldwell told Reuters by telephone.

The U.S. military said this month that two explosives vests were found in the zone. A suspected third vest was known to have been missing and a hunt was launched to find it.

An Iraqi official said another suspected bomb had been found nearby and detonated.

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The SITE Institute, a private U.S. organisation that tracks militant activity, questioned media reports that al Qaeda had claimed responsibility for the attack, saying the claim had been posted on a Web site not used by the group.

A Reuters cameraman said the blast took place at the cashier’s register in the cafe, near parliament’s assembly hall.

“I saw a ball of fire and heard a huge, loud explosion. There were pieces of flesh floating in the air,” said the cameraman, who was lightly wounded in the arm.

Militants have rarely carried out attacks inside the zone, although it has come under increasing rocket and mortar attack.

A rocket landed close to a building where Maliki and U.N. Secretary General Ban Ki-moon were speaking last month.

In the worst previous bomb attack in the zone, two al Qaeda bombers killed five people, including three Americans, in 2004.