At least forty-seven people were killed when two car bombs exploded in upscale districts of Algiers on Tuesday, a security source said, in the bloodiest attack since the 1990s on the capital of the OPEC member state.

There was no immediate claim of responsibility but commentators said it appeared the work of al Qaeda's north Africa wing, which claimed a similar bombing in downtown Algiers in April and other blasts east of the capital over the summer that have worried foreign investors.

One of Tuesday's blasts struck near the Constitutional Court building in Ben Aknoun district and the other close to the U.N. offices and a police station in Hydra, both areas where several Western companies have their offices, a source said.

Interior Minister Noureddine Yazid Zerhouni said a suicide attacker appeared to have detonated the Hydra bomb.

In Ben Aknoun people ran through the streets crying in panic and the wail of police sirens filled the air.

A body lay on the road covered with a white blanket, two buses were burning, debris from damaged cars was strewn across pavements while police struggled to hold back onlookers.

I want to call my family, but it is impossible. The network is jammed. I know they are very concerned as I work near by the council, a veiled woman working at a perfume shop said.

There was a massive blast, a U.N. worker wrote in an anonymous item for a BBC website.

Everything shattered. Everything fell. I hid under a piece of furniture so I wouldn't be hit by the debris... One of my colleagues had a big wound in her neck, she was bleeding severely.

Several of the casualties in Ben Aknoun were students riding a school bus, the official APS news agency said. The security source said the final death toll could go as high as 60.

Algeria, a major gas supplier to Europe, is recovering from more than a decade of violence that began in 1992 when the then army-backed government scrapped elections a radical Islamic party was poised to win. Up to 200,000 people have been killed in the subsequent violence.

FEARS

The violence has subsided since then but a string of attacks this year including the April 11 attack that killed 33 in Algiers has raised fears the country could slip back into the turmoil of the 1990s.

Some attacks or attempted attacks have occurred on the 11th of the month in what Algerians interpret as a form of homage to the September 11 attacks on the United States.

Western nations have expressed concern at militant islamist activity through the north African region and dependents of several western firms operating in Algeria have been repatriated over the past 12 months due to security worries.

Tuesday's attacks dented security forces' hopes that they had crushed the insurgency following the killing by the army of the ringleaders of the April 11 attacks.

French president Nicolas Sarkozy, who visited Algiers only last week, called the blasts barbaric and profoundly cowardly acts. Washington condemned the attacks and said it would continue counter-terror collaboration with Algeria.

Anis Rahmani editor of Ennahar daily and a security specialist told Reuters: Al Qaeda wanted to send a strong message that it is still capable despite the lost of several top leaders. Now the key problem is that social conditions are still offering chances for terrorists to hire new rebels.

This is a problem that must be tackled if we want to defeat al Qaeda.

To date the authorities have said the only way to put an end to 16 years of bloodshed is to pursue national reconciliation, a policy which grants amnesty to the al Qaeda-linked guerrillas in return for disarmament.

But commentators say the strategy takes no account of a bleak social background of unemployment and poverty that fuels discontent and aids recruitment of suicide bombers.

A deteriorating social climate marked by joblessness and abiding poverty posed a menace to stability, diplomats say, noting that unemployment among adults under 30 is 70 percent.

(Editing by Ralph Boulton)

Algeria