French police are questioning four people of North African origin arrested on suspicion of planning a chemical attack.

Interior Minister Nicolas Sarkozy said the three men, and the wife of one of them, had a large sum of money, fake documents, two vials containing unknown substances, and protective clothing.

This is not a petty affair Nicolas Sarkozy French Interior Minister

The items were seized on Monday in an apartment in the northern Paris suburb of La Courneuve.

French authorities have arrested more than 20 suspected Islamic militants in recent weeks and the country has been put on a state of high alert.

Mr Sarkozy, who described the case as "very serious", said the protective suit was designed for chemical or biological attack.

One vial was labelled "iron perchloride" and the liquid it contained has been sent for analysis, media reports say.

Iron perchloride is normally used for engraving computer circuit boards, but mixed with other chemicals can be used to make poison.

"When one finds people with this sort of material, one has to arrest them," said Mr Sarkozy. "This is not a petty affair."

'Chechnya link'

Police said they also seized $5,000 in cash, Islamist propaganda, and a computer from the apartment.

Three of those arrested are of Algerian origin and the other is Moroccan.

Mr Sarkozy told parliament on Tuesday that the suspects were thought to have spent time in Chechnya and that one had links with Rabah Kadre, being held in the UK on terrorism-related charges.

"Even before we know the precise results of the analyses (on the products seized), it was better to arrest them before rather than wait until after," he said.

He said the four were also believed to have spent time in Afghanistan.

Under French anti-terrorism laws, they can be held for up to four days after which they must be placed under formal investigation or released.

Extra security

The French Government has ordered an extra 1,000 police and troops on to the streets of the capital over Christmas.

Monday's arrests were made as part of an investigation by France's leading anti-terrorist judge, Jean-Louis Bruguiere.

He was also behind the arrest last month of a group of people in Paris suburbs accused of having had links to the shoebomber Richard Reid - a British man who attempted to blow up a flight from France to the US with explosives in his shoes.