PARIS: French police arrested four suspected Islamist militants near Paris on Tuesday as part of an investigation into the recruitment of volunteers by Al-Qaeda insurgents in Mali, Interior Minister Manuel Valls said.

The arrests came as France's intervention in Mali to rid its former colony of Islamist fighters has prompted the authorities to increase security measures against possible reprisal attacks on its interests in mainland France and abroad.

Anti-terrorism judge Marc Trevidic, who is in charge of the operation, told Reuters last month that France needed more robust local policing, better intelligence sharing and the ability to infiltrate small radical Islamist groups if it hopes to fight new security threats on its soil..

He has said the insurgency that seized the north of Mali was paving the way for attacks on France as more French Muslims of African origin were finding a cause in the conflict.

Three of the four men arrested were Franco-Congolese and one was Malian, a police source said.

"There is an operation ongoing in the Paris region, conducted by the DCRI (domestic security service), which comes after the arrest of an individual a few months ago on the border between Mali and Niger," Valls told BFM TV.

That man was a Franco-Congolese social worker named Cedric Lobo, 27, who was arrested in Niamey, the capital of Niger, while attempting to purchase a four-wheel drive vehicle with a false driver's license, the police source said.

Lobo was attempting to reach the historic Malian city of Timbuktu to join Al-Qaeda in the Islamic Maghreb (AQIM) when he was detained by Niger police, the source said.

He was subsequently extradited to France, where he was charged with planning attacks and remanded in custody.

ISLAMIST NETWORKS

Valls said the arrests had come after a long investigation into Al-Qaeda recruitment rings led by Trevidic.

French anti-terrorism judges have opened several preliminary investigations in the past year involving individuals suspected of links to Malian "terrorist" cells.

"We have to continue dismantling these networks that want to either commit attacks on our soil or take individuals overseas to carry out jihad," Valls said.

He added that police had stopped several individuals trying to travel from France to the Sahel - a vast swathe of semi-arid territory stretching from Senegal in the west to Eritrea in the east - known as a base for traffickers and Islamist militants.

Valls said a "handful" of French nationals had already joined Al-Qaeda-linked groups.

"There is no direct threat, but there are threats on the Internet, on social networks, calling on people to wage war, to attack French interests," Valls said.

France has tightened security in public buildings and on public transport, although it has kept its security alert level at red, signifying "probable threats", one down from the scarlet level which means "definite threats".

Highlighting the threat overseas, Paris has raised its travel warning for its citizens across the Muslim world.

The embassy in Tunis on Monday confirmed that a French school in the Tunisian capital had been sprayed with graffiti warning of reprisals after France's intervention in Mali.