PARIS - French police have released without charge 10 suspected Islamists arrested in pre-dawn raids two days ago, the second such swoop in less than a week, a judicial source said on Friday.

Of 10 alleged extremists arrested Wednesday, four were released on Thursday and the remaining six walked free on Friday, the official said.

Wednesday’s raids were carried out in the southern port city of Marseille as well as Roubaix near the Belgian border, and in several other locations in the country’s south and southwest.

They came less than a week after 19 alleged Islamists were arrested in similar anti-terrorist swoops on Friday. Prosecutors have announced that they will seek terror charges against 13 of them.

French authorities have vowed a crackdown on Islamist extremists after self-confessed Al-Qaeda follower Mohamed Merah was shot dead in a police siege following a killing spree in which he murdered seven people.

The killings came just weeks before France’s hotly contested presidential election, with security a major campaign theme and President Nicolas Sarkozy closing the gap in opinion polls on his rival, Socialist Francois Hollande.

Sarkozy’s camp has been accused by some of its opponents of exploiting fears and stage-managing militant arrests for political gain.

Whereas, France’s interior minister says some Islamist groups in France want to avenge the death of a Muslim radical, who the government says was responsible for the killing of seven people in a shooting spree in the country’s south.

Claude Gueant, speaking on French radio Europe 1 Friday, said that authorities have observed increased “desire” and “enthusiasm” among such groups to avenge the death of Mohamed Merah, a Frenchman of Algerian descent, killed in a standoff with police last month.

President Nicolas Sarkozy, who is facing a tough re-election in a presidential vote, with a first round April 22, has put security high on his agenda.

Gueant called on the people to be “vigilant and attentive.” French security agencies are already on edge and have carried out sweeps, detaining 10 people from five cities Wednesday in the latest roundup. Four of them were released Thursday after questioning and a judicial official said that the other six would be released late Friday. The official was not authorized to speak publicly and asked not to be named.