They are suspected of obtaining "equipment" for Ahmedy Coulibaly, who shot dead a policewoman on the outskirts of the French capital before taking hostages at the store a day later, prosecutor Francois Molins said.

Three of the men, who are all in their twenties, have criminal records and at least one met Coulibaly in prison, he added.

All four are being held in custody while further inquiries are carried out.

They have been named only as Willy P., Christophe R., Tonino G. and Mickael A.

Mr Molins said three are believed to have procured weapons and tactical material for Coulibaly, but are not accused of complicity in the supermarket attack.

The DNA of Mickael A. was found on a revolver in Coulibaly's apartment and on a glove he wore in the store. It is claimed Mickael A. had 18 phone contacts with Coulibaly on 6 January.

The lawyer for one of the suspects said his client was unaware of any terrorist plot and was afraid of Coulibaly, who "terrorised" him and intimidated him into helping.

Mr Molins said authorities in France are working with other countries to track down other possible accomplices

Police are also investigating who edited and released a video of Coulibaly on the internet several days after he and the two Charlie Hebdo gunmen were shot dead by officers.

In the video, Coulibaly pledged allegiance to the Islamic State group, which has seized control of large areas of Syria and Iraq.

Mr Moulins said police believe the attacks on the supermarket and satirical magazine Charlie Hebdo, carried out by brothers Said and Cherif Kouachi, were coordinated.

Anti-terrorism measures

Security in France and other European countries including Belgium and the UK has been stepped up following the atrocities.

French Prime Minister Manuel Valls has announced an extra 2,600 intelligence staff are to be hired to combat the growing threat of jihadists, with almost 3,000 people now involved in "terrorist networks".

He said they would be taken on over the next three years at a cost of €425m.

The French President has also announced he is scaling back planned job cuts in the country's army following the terror attacks in Paris.

Francois Hollande says 7,500 fewer posts will be axed.

His government originally wanted to reduce the size of the army by 26,000 come 2019.

Mr Valls said France would also bolster its intelligence apparatus, introducing a measure to make it easier to tap phones.

Interior Minister Bernard Cazeneuve, meanwhile, revealed Islamic extremist hackers have claimed responsibility for more than 1,300 attacks on French civilian and military websites since the Paris killings.

Overnight on Wednesday, the Twitter feed of Le Monde newspaper was hacked by the Syrian Electronic Army, a group that aligns itself with Syrian President Bashar Assad.

Originally posted at 9.30am