PARIS -- Armed soldiers and police, some in camouflage uniforms and toting automatic weapons, stepped up patrols at major tourist sites, train stations and shopping malls as French authorities raised the spectre of a potential terrorist attack by militant Islamists reminiscent of the series of deadly bombings that rocked Paris in the mid-1990s.

The heightened security in the capital, where thousands of people were evacuated just last week from the iconic Eiffel Tower after a bomb hoax, is a response to specific intelligence reports of at least one plot in the works, according to security officials.

Media reports cited police sources saying that Algerian and other intelligence sources told France they had credible information that a suicide bomb attack was being planned against the public transit system.

Interior Minister Brice Hortefeux gave no specifics but said, "The threat is real."

One sign that the terror threats were being taken especially seriously was a decision to provide an armed security detail to protect Dalil Boubakeur, the rector of the biggest mosque in Paris.

Mr. Boubakeur said he had not asked for protection and did not feel he was in danger. "I asked whether there is information about a threat to me in particular, and they said no, that it was a general threat," he told reporters.

The ratcheting up of security and terror warnings inevitably recalled the last big wave of terrorist attacks in France in 1995 and 1996. A militant Islamist group based in Algeria was blamed for six separate bombings, in Paris and Lyon, on commuter trains and a Jewish school. The first of the bombings was preceded by the assassination of a moderate Algerian imam living in Paris.

Mr. Boubakeur referred to that murder and the bombings that followed in a radio interview. If the terrorism threats are real, he said, "then it makes sense to take similar measures as were taken at that time."

Uniformed soldiers carrying automatic weapons patrol not just airports and train stations but also the financial centre of La Défense and the Montparnasse tower.

Security was increased after an anonymous phone call last Thursday warned of a bomb at the Eiffel Tower.

Thousands of people were evacuated from the popular tourist site and the park nearby, as well as from Saint Michel suburban rail station in the crowded Left Bank that was the target of one of the bombs 15 years ago.

The same day, armed men kidnapped five French people and two Africans working for the state-owned nuclear reactor company Areva in the northern desert region of Niger.

Although no one has yet claimed responsibility, French officials said they are treating the abductions as the work of a North African Islamist group calling itself al-Qaeda of the Islamic Maghreb.

The same shadowy group, operating in western Africa, has issued increasingly vitriolic threats to France, most recently last month after French forces killed several suspected militants at one of its bases in northern Mali. The attack was an attempt to free another French hostage who was subsequently executed.

In a video message, a leader of the group said President Nicolas Sarkozy had "opened for his country the gates of hell."

Jihadist videos posted on the Internet in recent weeks have specifically named France as an enemy, according to Bernard Squarcini, the head of French counterintelligence.

In a series of interviews over the weekend with French reporters, he said that intelligence officials had received credible and consistent information about imminent threats from different sources. "All the lights are flashing red," Mr. Squarcini said.

France is a particular target because the group has its roots in Algeria, a former French colony, and because French troops are deployed in Afghanistan, he added, and its punitive approach to Muslim head scarves "attracts the interest of certain radical Islamic movements."

Last week, the French Senate voted to make it a crime to wear a full face-covering veil in public places, confirming an earlier vote by the National Assembly. France also prohibits the wearing of Muslim head scarves and other religious gear in public schools, and was condemned by some Islamist groups when that law was passed in 2004.