France has reinforced its already high state of alert after Saudi Arabian intelligence officials warned Paris there was a "real" threat of an imminent terrorist attack by an offshoot of al Qa'eda.
The heightened risk, which is being treated as distinct from previous indications that France is a current target for radical groups, was disclosed by the French interior minister, Brice Hortefeux.
Mr Hortefeux was vague about when the new information from Saudi sources had been received, saying it arrived "in the last few hours, few days". He was speaking on a weekly discussion show on Sunday presented jointly by French television, radio and the daily newspaper Le Figaro,
But the warning from Mr Hortefeux was clear enough: al Qa'eda in the Arabian Peninsula (AQAP) was "without a doubt active, or aimed to be active" and posed a threat to the European continent generally "and notably France".
"This is not about overestimating the threat or underestimating it," Mr Hortefeux said. "I am indicating, based on all these elements, that the threat is real."
In the Saudi capital Riyadh, authorities declined to elaborate on the information passed to Paris. "We do not comment on intelligence matters," said Gen Mansour al Turki, spokesman for the Saudi interior ministry.
Neverthless, the security alert is evidence of increasingly transparent sharing of intelligence among countries facing terrorist threats on a broad front. It is linked to recent arrests by the Saudi authorities in their battle against AQAP, the group established at the beginning of last year by Yemeni activists and Saudis formerly held by the United States at Guantanamo Bay.
It is believed to have been responsible for a suicide bombing aimed at the British ambassador in Yemen, Timothy Torlot; a rocket attack on his deputy, Fiona Gibb; and the failed attempt by a Nigerian student based in London to blow up a plane over Detroit last December.
France has avoided serious attacks on its territory since 1995, when the Algerian Armed Islamic Group (GIA) carried out a series of bombings.
Any hope that strong opposition to the war in Iraq would spare the country from terrorist attacks has proved ill-founded. Islamist groups have been quick to seize on such issues as French involvement in the conflict in Afghanistan and the ban on the face-covering veil as evidence of anti-Muslim policies.
In recent years, French security agencies claim to have thwarted a number of other planned attacks. Since the beginning of September, the country has been in a state of enhanced vigilance after information from Algeria suggested a female suicide bomber was preparing to detonate a device on a public transport target. As tension increased, and government ministers stressed the need for extreme alertness, the Eiffel Tower was twice evacuated because of bomb scares. Reports in the western media have also spoken of plans for attacks in Paris and other European cities comparable to the killings of 166 people by gunmen at a Mumbai hotel in 2008. Several European countries are regarded as vulnerable to attack.
The UK has raised from "general" to "high" its level of alert for travellers to Germany and France, and people heading in the opposite direction have received similar warnings from their own countries. The UK foreign office states in its advice to British nationals proposing to visit France: "Like other large European countries, the French authorities continue to consider that there is a high threat of terrorism. Attacks could be indiscriminate, including in places frequented by expatriates and foreign travellers."
Despite the high state of alert and the renewed focus on the Yemen-based AQAP, some analysts question the ability of the group to carry out an attack in Europe. "I'm not dismissing it, but it sounds a bit strange," said Mustafi Alani, the director of security studies at the Gulf Research Center, which is based in Dubai. The al Qa'eda affiliate is "over-stretched and under lots of pressure" from Yemeni and Saudi authorities, he said, as well as from the United States. Since the unsuccessful attempt to blow up an American passenger jet, Washington has poured intelligence and military resources into the impoverished Yemeni nation in support of its security forces.
Mr Alani was also doubtful about the reports because operational responsibility for Europe - at least in the past - rested with al Qa'eda affiliate in North Africa, known as al Qa'eda Organisation in the Islamic Maghreb. "Targeting Europe is theoretically the responsibility of the North African command. It's not the Yemeni command," he said. He described al Qa'eda as divided since 2006 into four "commands", each responsible for operations in a specific geographic area. AQAP's main responsibility was the Arabian Peninsula, with high priority on attacks in Saudi Arabia.
Mr Alani gave as an example last year's attempted assassination of Prince Mohammad bin Nayef, a deputy interior minister. Of the other known "commands", one was intended to operate in Iraq, Jordan and Syria while the other was responsible for Afghanistan and Pakistan. Even so, Mr Alani noted that "the Yemeni command is emerging as a highly skilful command", as shown by the attempted assassination of Prince Nayef and the aircraft bomb plot.
The French government is adamant that it is not over-dramatising the risk. The defence minister, Herve Morin, told the newspaper Le Parisien this month: "The terrorist threat exists, and could strike us at any time. Networks organising attacks are constantly being dismantled around the world and it is good that the French know it."