(Adds mass kidnapping claim)

By Sami al-Jumaili

KERBALA, Iraq, April 14 (Reuters) - A suicide car bomber killed at least 40 people and wounded scores at a crowded bus station near a Shi'ite shrine in the Iraqi holy city of Kerbala on Saturday, police and hospital sources said.

In Baghdad, police said a suicide car bomber detonated his device near a checkpoint at the southern Jadriyah bridge, killing 10 people and setting fire to cars in the second major attack on a bridge in the capital in the past three days.

Television footage of the aftermath of the Kerbala explosion showed a distraught man cradling the charred body of a small child, and witnesses said the blast sent body parts flying into the air. Ambulances rushed to the scene.

"I suddenly heard a horrifying explosion. I had never expected that Kerbala would see an explosion of that size because it is a safe city," said Ali Mussawi, 30, a store owner who was 50 metres (yards) from the blast.

Shortly afterwards, Iraqi police fired into the air to disperse protesting crowds who blamed local authorities for failing to provide security.

As U.S. helicopters buzzed over Kerbala, 110 km (70 miles) southwest of Baghdad, authorities imposed an indefinite curfew.

The attack occurred near a crowded market 200 metres from the Imam Hussein shrine, where the grandson of Islam's Prophet Mohammad is buried in one of Iraq's holiest cities.

Attacks at or near shrines are highly provocative. The bombing of a Shi'ite shrine in Samarra in February 2006 unleashed sectarian violence that has pushed Iraq to the brink of civil war.

Khaled al-Rubaie, media director of Kerbala's al-Husseini hospital, said 41 people had been killed and 138 wounded, many of them women and children.

Earlier, a police source put the death toll at 65 while Salim Katham, media director of Kerbala's health directorate, had said 32 people were killed.

In a possible mass kidnapping, a group linked to al Qaeda said it had abducted 20 Iraqi soldiers and policemen and demanded the release of all Sunni women held in Iraq's prisons, according to a Web statement.

The Internet posting by the self-styled Islamic State in Iraq carried pictures of rows of blindfolded men, most of them in either blue or brown uniforms, in front of the group's black banner. Their hands appeared to be bound behind their backs.

The statement said the 20 men of various ranks were abducted northeast of Baghdad. It did not say when they were seized.

Officials could not be reached for comment.

BAGHDAD BRIDGES

Baghdad's Jadriyah bridge escaped the Saturday bombing without structural damage, but people nearby were not so lucky. Charred corpses were piled in the back of an ambulance, and a badly burned body lay on the bridge.

Two days earlier, a truck bomb killed seven people on the capital's Sarafiya bridge, destroying most of the steel structure in an attack the speaker of the Iraqi parliament, Mahmoud Mashhadani, called a conspiracy to split the city.

A dozen bridges cross the Tigris in Baghdad, linking the east and the west of the capital.

A two-month-old, U.S.-backed security crackdown in Baghdad has reduced the number of targeted killings, but U.S. and Iraqi commanders still find car and suicide bombers hard to stop.

On Thursday, a suicide bomber penetrated the restaurant of the Iraqi parliament in the fortified Green Zone, killing a lawmaker and wounding two dozen other people in the most serious breach yet of Baghdad's most secure area.

In the southern city of Basra on Friday night, British forces killed eight gunmen who were placing landmines close to where four British soldiers and their translator were blown up earlier this month, the military said.

British forces in southern Iraq are pursuing a more aggressive policy towards Shi'ite militias as they prepare to hand over security control of Basra to Iraqi security forces later this year. (Additional reporting by Yara Bayoumy, Mussab Al-Khairalla and Ross Colvin in Baghdad)

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