French anti-terror prosecutors are seeking to charge four men in connection with the attacks in Paris that left 20 people dead.

They would be the first suspects charged in the country's bloodiest terrorist attacks in decades.

The four men awaited an anti-terror judge's decision early today on whether to open preliminary investigations against them.

The possible charges were expected just hours before the French government was to unveil new measures aimed at helping head off future attacks, giving police more power to tap phones, monitor websites and force Internet companies to block messages of hate posted online.

Prime minister Manuel Valls will present new security measures today that will include efforts to increase intelligence-gathering against jihadis and other radicals, block their activities on the Internet, and prevent them from collaborating inside prisons or travelling abroad to fight.

France is on high security alert after the country's worst terrorist attacks in decades. The court case and the arrests came as Mr Valls urged his nation to do some soul-searching about the country's deep ethnic divisions and declared that fighting hatred, anti-Semitism and racism was a top priority, especially in France's impoverished housing projects.

The Paris prosecutor's office said the four men in court yesterday were suspected of providing logistical support to Amedy Coulibaly, one of the terrorists killed by police, and requested they be detained longer on weapons and terrorism charges.

Coulibaly shot a policewoman to death on the outskirts of Paris and then killed four hostages inside a kosher supermarket before being shot dead by police.

It is not clear whether the four suspects, all in their 20s, were involved in plotting the attacks or even aware of Coulibaly's plans.

No one has been charged with direct involvement in the January 7-9 Paris terror attacks. Coulibaly claimed allegiance to Islamic State while the two brothers who attacked the Charlie Hebdo satirical weekly said they were backed by al Qaida in Yemen.

In Bulgaria, a court yesterday agreed to extradite a Frenchman who knew one of the two Kouachi brothers who massacred 12 people at the newspaper.

Fritz-Joly Joachin told the Bulgarian court he was innocent and wanted to return to Paris to clear his name.

Five others arrested in the investigation of the terror attacks in France were released without charge, prosecutors said.

Meanwhile, France honoured a Mali-born employee of the kosher market who saved lives there, by granting him citizenship.

Lassana Bathily, 24, was in the store's underground stockroom when Coulibaly burst in upstairs and killed four people.

He turned off the freezer and hid a group of shoppers inside before sneaking out to speak to police and help the operation to free the 15 hostages and kill the attacker.

Mr Bathily has lived in France since 2006. He had filed an application for French citizenship last year.

Mr Valls told journalists that the attacks should force France to look at the "apartheid" within.

The conservative Socialist whose hard line on Islamic extremism has won many fans said he was not making excuses for crime or terrorism, "but we also have to look at the reality of our country".

He said memories have dimmed of the three weeks of riots by disaffected youths in 2005 that shook France.

"And yet, the stigmas remain ... a territorial, social and ethnic apartheid that has imposed itself on our country," he said.

In response to the 2005 riots, the French government spent hundreds of millions of pounds to improve conditions in its rundown suburbs, with little success.

Unemployment among young people in the housing projects is well above the national average and state buildings are often targeted for vandalism and arson.

French authorities also arrested five ethnic Chechens from Russia yesterday in raids in southern France, including one whom a mayor said was found with a cache of explosives.

The authorities said the men had no established links to terrorism but did have ties to other crimes.

In Athens, an Algerian man suspected of jihadi terrorist links in Belgium appeared before a Greek prosecutor for an extradition hearing on being sent to Belgium.

The suspect, whose name was not released, was detained on Saturday in Athens, where he lives.

Belgium launched a large anti-terrorism sweep last week, during which two suspects were killed and one wounded, that netted several returnees from Islamic holy war in Syria.