French police arrested four suspected Islamist militants near Paris on Tuesday as part of an investigation into the recruitment of fighters for al Qaeda-linked forces in Africa's Sahel, Interior Minister Manuel Valls said.
The arrests are the first since France intervened in Mali last month to repel an offensive by Islamist rebels, which has raised concerns about possible reprisal attacks on French interests at home and abroad.
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.
He was subsequently extradited to France, where he was charged with planning attacks and remanded in custody.
Valls said the arrests had come after a long investigation into al Qaeda recruitment rings led by anti-terrorism judge Marc Trevidic.
French President Francois Hollande last month instructed his Prime Minister Jean-Marc Ayrault to tighten security in public buildings and on public transport in, though France kept its security alert level at red, signifying "probable threats", one down from the scarlet level which means "definite threats".
"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.
He added that police had stopped several individuals trying to travel from France to Africa's Sahel region, known as a base for traffickers and Islamist militants.