PARIS - France is adding hundreds of police to Paris streets and stepping up checks at train stations and large shops after a previously unknown group claimed it planted explosives at a major department store, the interior minister said yesterday.

Michele Alliot-Marie said the sticks of dynamite discovered Tuesday at the Printemps store in Paris appeared old and relatively common - of the type "that could be found on construction sites, for example."

The "Afghan Revolutionary Front," a name not previously known to French police and intelligence officials, said it planted the sticks, which lacked detonators. A letter sent to a French news agency warned that if France's 2,800 troops in Afghanistan were not pulled before the end of February, "we will go back into action in your big capitalist stores and this time without warning."

Defense Minister Herve Morin said yesterday that Islamic extremists were not the main focus of the investigation. He told RTL radio that the letter did not fit the profile of Islamic radicals.

"The word


in the group's name, the word


to designate the stores, the lack of reference to Islam or jihad in effect add up to the fact that the Islamist trail isn't the first trail," he said.

Alliot-Marie ordered 700 more police in Paris patrols, atop 1,500 deployed about two weeks ago as part of annual security measures during the seasonal shopping rush. Other cities will also get extra patrols, she said.

Authorities and security guards will conduct enhanced searches of department stores and rail stations before they open, she said, and some stores will reduce the number of entrances "to better channel customers." Guards at Printemps checked customers' bags yesterday morning at the store's entrance.

Police are reviewing video from the store and from the post office where the letter was posted, Interior Ministry spokesman Gerard Gachet said.