It was the most serious incident in an Algerian city since triple suicide bombings in the capital Algiers in April, claimed by al-Qaeda, killed 30 people and injured 220.

Call to vote

Security officials said they believed the bombs were meant to have been planted at a nearby market but officers intercepted the bomber, who dropped the bags and escaped.

But an eye witness said that one of the bombs went off in his hands.

Yazid Zaerhouni, Algeria's interior minister, condemned the blasts as "an act of sabotage against the Algerian democratic system".

He also urged Algerians to go to the polls on Thursday in big numbers "to show their attachment to democracy".

"The best way to respond to such attacks is a strong turnout for the parliamentary elections," Zaerhouni said on Algerian public radio.

Heightened security is expected for the upcoming National People's Assembly elections.

Shutdown ordered

Algeria's interior ministry has ordered trucks to stay off the roads and markets to be closed.

In a recording aired this week by Al-Jazeera television, al-Qaeda called on Algerians to snub the polls, which are expected to see political parties aligned with Abdelaziz Bouteflika, the president, to retain a majority.

"These elections are nothing but a farce that is not different from other farces seen before in Algeria," said Abu Mussaab Abdul Wadud, leader of al-Qaeda in North Africa.

"If you take part in these elections, you will be sharing those apostates' flagrant act," he said in the audio tape aired on Monday.

"Express your opinion and renounce these elections. You only need to boycott or abstain from voting."

'Deepen democracy'

Politicians are concerned by the lack of enthusiasm for the parliamentary elections among Algeria's 18.3 million registered voters.

"Democracy cannot be created if one turns his back on the ballot box," Abdelaziz Belkhadem, the Algerian prime minister, told AFP.

"Choosing between political parties and programmes is not just a civic act, but a way to deepen democracy."

The National People's Assembly, in which the National Liberation Front (FLN) holds the most seats, is seen by Algerians as a flaky body.

Bouteflika, first elected in 1999, is due to step down at the end of his current second term.