A group of 18 people were murdered Sunday, allegedly by armed Islamists, at a roadblock set up in the town of Boumedfaa in the northwest of the country, the official APS news agency reported.

Another nine people were slaughtered in a similar ambush the day before near Boufarik, just south of the capital, witnesses said. The witnesses allegedly said Islamists were responsible.

The killings bring the death toll over the week to more than 50, and to more than 150 so far for November, according to the media.

Last week, an armed group killed 18 people at another false checkpoint about 30 kilometers from Boufarik.

The rash of violence comes less than two weeks before the start of the fasting month of Ramadan, which in recent years has repeatedly seen heightened violence by Islamists who consider the period opportune for their jihad.

Witnesses said that those killed had been aboard a bus that stopped by the checkpoint. The killers set fire to the vehicle before fleeing.

The exact same tactic was used in Saturday's attack, which claimed the lives of two women and two children, witnesses of that ambush said.

Some 15 assailants dressed as civilian guards working for the government set up the checkpoint - a method frequently used by the Islamists - and stopped two cars, killing the passengers before setting the vehicles alight, the witnesses allegedly said.

Genuine civilian guards rushed to the scene on hearing the gunfire, and the attackers fled.

Another recent attack was staged on November 15, when 19 villagers - 13 of them children -- were killed with axes and shovels in Ouled Djilali-Benyahia, in the northwest of Algeria.

But the killing of one man last week was the most damaging to efforts by President Abdelaziz Bouteflika to bring peace to Algeria after seven years of brutal civil war that has claimed more than 100,000 lives.

Abdelkader Hachani, the number three of the banned Islamic Salvation Front (FIS), was shot dead on November 21 in his dentist's waiting room.

Hachani was a key political figure who paved the way for a massive FIS lead in the first round of parliamentary elections in December 1991. The army stepped in the following month to prevent the second round from taking place.

The cornerstone of Bouteflika's campaign is a law, overwhelmingly approved in a national referendum in September, under which Islamic militants who surrender to the authority of the state may apply for partial or full amnesty.

Interior Minister Abdelkmalek Sellal on Saturday called on "citizens and businesses" to be "more vigilant" at the approach of Ramadan. "The security services cannot deal with the killings and acts of sabotage on their own," he said.