A spate of arrests of suspected Islamic terrorists and rising security-alert levels in Europe point to heightened fears here of a Christmas attack on European soil, in the wake of last month's bombings in Istanbul.
The authorities say they have no specific information about an imminent strike. But the approach of the holiday season and increasing "chatter" among suspects have raised the alarm in several major European capitals.
"The networks that had been hunted and disorganized have started to reorganize," says Alexis Debat, a former French counterterrorism official who maintains close links with French intelligence services. "The attacks on British interests in Istanbul sent a very strong message that these networks are still alive and still consider Europe a prime target."
British police last week, for the first time, arrested a suspected jihadi, or holy warrior, in possession of explosives. British Home Secretary David Blunkett said Sajid Badat posed "a very real threat to the life and liberty of our country."
Mr. Badat, one of more than 20 people arrested since last week in a series of antiterrorism raids in Britain, was charged with conspiring with Richard Reid, the "shoe bomber" who tried to blow up a plane flying from Paris to Miami in 2001.
In Germany, police arrested three men of North African origin last Friday on an Italian warrant, including one suspected of recruiting fighters for operations against US troops in Iraq.
And the British government recently upgraded its security alert to "severe general," its second-highest level, while the French authorities raised their alert level one step on Monday.
In the wake of the Istanbul bombings, Germany has increased already tight security around the US and British embassies in Berlin, sealing off roads around the buildings, amid worries that the war in Iraq is galvanizing radical Islamists in Europe.
"It is not a mass movement, but there are links in Europe," says Udo Steinbach, director of the Institute for Middle East Studies in Hamburg. "The intelligence services are alarmed."
The mayor of London, Ken Livingstone, told a conference last weekend that police had recently "intercepted four attempts that were being planned to actually cause mayhem and take life in this city." He gave no further details. London police commissioner Sir John Stevens said Wednesday that his force was on a heightened state of terrorist alert.
Christmas is seen as a particularly vulnerable time in Europe, according to Claude Moniquet, who heads the European Strategic Intelligence and Security Center, a think tank in Brussels. "There are sure to be lots of people in the street, which means higher casualties, and then there is the religious aspect," he says.
Several holiday-timed plots have been thwarted in the last four years: In 1999, Ahmed Rezam was arrested at the US-Canadian border, on his way to bomb Los Angeles airport; on New Year's Eve in 1999, Jordan foiled a plot targeting millennium celebrations; in 2000, a group linked to Al Qaeda planned to bomb the Christmas fair in Strasbourg, France; in December 2001, Richard Reid was arrested before trying to blow up a plane; and last year, in late November, police in London and Paris foiled a plan to poison the London underground with cyanide.
Since Sept. 11, 2001, Mr. Debat points out, Al Qaeda or groups sympathetic to it have struck successfully only in countries where the police are relatively inexperienced in counterterrorism, such as Turkey, Morocco, and Kenya.
European nations, with more resources, also have more practice: Italy quelled the Red Brigades, Germany dealt with the Baader-Meinhof gang, France rolled up the Algerian "Armed Islamic Group" networks, Spain has battled the Basque separatist ETA for many years, and Britain fought the IRA for decades.
At the same time, says Debat, "the level of cooperation between the European intelligence services is higher than it has ever been before," aiding the arrest of some 200 Al Qaeda suspects in Europe since the World Trade Center attacks.
But leading European nations, several of whom have sent troops to work alongside US forces in Iraq, remain prime targets for radical Islamists, especially Britain, which has identified most closely with the United States.
Abu Mohammed al-Ablaj, an Al Qaeda spokesman, warned in a communiqué last May that mujahideen "wearing explosive belts" would attack "American and Western cities," and a radical Egyptian-born cleric in London, Abu Hamza, declared last month that Britons were "sitting ducks" for suicide bombers.
Complicating the European security forces' task is a pattern that has emerged in recent attacks in Morocco, Saudi Arabia, Indonesia, and Turkey: The bombers were local men. Most European nations have large Middle Eastern and Muslim communities - many of whose members hold European passports - which makes potential bombers among them harder to track than foreigners would be.
Of the 15,000 to 30,000 "jihadis" whom terrorist experts believe to exist worldwide, about 10 percent are thought to hold passports from European Union member states, according to Mr. Moniquet.
"You always had national components of Al Qaeda because of its very nature" as an international network, says Magus Ranstorp, a terrorism expert at St. Andrew's University in Scotland. "What is different today is the scale and scope of suspects who are European Union nationals."
European intelligence services "are very aware that there are several hundred operatives in Europe capable of carrying off" a major attack, adds Debat.