FRANKFURT, Sept. 5 — German authorities said Wednesday that they had stopped a major terrorist attack against American and German targets in this country, arresting three Islamic militants and seizing a large amount of potentially explosive chemicals and military-grade detonators.
Those arrested — two German citizens who had converted to Islam and a Turkish resident of Germany — were in the advanced stages of plotting bomb attacks that could have been deadlier than those that killed dozens in London and Madrid, the police and security officials said. At least five lesser figures are still being pursued, they said.
“They were planning massive attacks,” the German federal prosecutor, Monika Harms, said at a news conference, outlining an intensive six-month investigation. She said the suspects had amassed hydrogen peroxide, the main chemical in the explosives used in the London suicide bombings of July 2005.
For months, Germany has been warning of a likely terrorist attack, and the government has been contemplating tightening surveillance and enforcement tactics that are now looser than elsewhere in Europe, in part because of Germany’s troubled 20th-century history.
Although officials spoke with confidence of the attack’s imminence and seriousness, they did not make fully clear the basis of their assertions. Europe has been the site of a number of devastating terrorist plots, but some have turned out later to be less than met the eye when announced.
If the announced details hold up under scrutiny, it means that Germany, like Britain, has become a target for sophisticated homegrown terrorism, and the case will fan the debate over the balance between civil liberties and public security. Previous German plots have been far smaller, masterminded by foreigners, or focused outside of Germany, like the 9/11 attacks, which were hatched in Hamburg.
An American intelligence official said that the United States helped German authorities track the location of two of the German suspects by eavesdropping on their cellphone conversations as they moved out of training camps in Pakistan.
Ms. Harms also said that the two German converts had trained in terrorist camps in Pakistan and that the three suspects had about 1,500 pounds of hydrogen peroxide, which they were preparing to move by van when arrested in an out-of-the-way village in western Germany on Tuesday afternoon. Security authorities in Europe have warned for some years that radical converts could pose a keen risk since they blend in easily to mainstream society.
The Turkish links in this case also trouble counterterrorism experts, who note that Germany has generally not had to contend with a radical element in its large Turkish Muslim minority.
“This is the first time I’ve seen a Turkish-German network,” said Guido Steinberg, a researcher at the German Institute for International and Security Affairs in Berlin. “And the fact that it is connected to a Turkish network in Pakistan is an even bigger problem.”
While the suspects were homegrown, the targets the authorities said they intended to attack were symbols of the enduring American presence in Germany.
Information that surfaced during the investigation, which included monitoring phone calls and tracking suspects’ movements, led the authorities to conclude that among the targets under consideration were the Ramstein Air Base, a crucial transportation hub for the American military, and Frankfurt International Airport.
The 12 vats of hydrogen peroxide collected by the suspects, when mixed with other chemicals, could produce a bomb with a force equal to 1,200 pounds of TNT, officials said.
“This would have enabled them to make bombs with more explosive power than the ones used in the London and Madrid bombings,” said Jörg Ziercke, head of the German Federal Crime Office.
Mr. Ziercke said the men belonged to a terrorist group that the police suspected of having close ties to Al Qaeda, though he did not offer evidence of those links. Counterterrorism experts here expressed wariness, noting that in almost every major attack or suspected plot since 9/11, the role of Al Qaeda has been raised but rarely substantiated.
Nevertheless, the German defense minister, Franz Josef Jung, said on state television, “There was an imminent security threat.” And some officials said the attacks could have come within days, noting that the German Parliament will soon take up a politically fraught debate about extending the deployment of German troops in Afghanistan. Next week is also the sixth anniversary of the 9/11 attacks.
German officials were visibly relieved by the arrests — the fruits of an elaborate investigation involving more than 300 people. On Wednesday, police officers raided 41 houses and apartments across Germany, seizing computers and other evidence.
German special forces police officers escorting a suspect from the German Federal Court of Justice in Karlsruhe today.
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Wolfgang Ratta/Reuters
One of the suspects, left, with German special police officers today.
But some politicians warned that the danger remained high. “The arrests yesterday are just evidence of how serious the situation here in Germany is,” said Wolfgang Bosbach, a prominent legislator in Chancellor Angela Merkel’s party.
The surveillance was so close that in July, officials said, the police managed to swap some of the tanks of hydrogen peroxide the suspects had gathered with tanks of a far lesser concentration.
One of the suspects, whom police sources identified as Fritz Gelowicz, a 28-year-old German born in Munich, was detained in 2005 in a raid in a Muslim neighborhood in Bavaria. He was put under surveillance again in December 2006, after he was seen scouting an American military barracks in Hanau, according to court documents.
The police are investigating a German-Turkish man, an associate of Mr. Gelowicz’s and also a suspect in the plot, two security officials said. They said he was believed to be in Turkey.
Tuesday’s arrests were made at a vacation home in Oberschledorn, a village of 800 tucked into the hills, 75 miles north of Frankfurt. The suspects had rented the house to store chemicals to make explosives, officials said. They were preparing to leave when the police swooped in.
One of the three men fled and, in a scuffle with a police officer, wrested a pistol from his holster and shot him in the hand before he was subdued, officials said.
A few had seen three young men walking through the village in recent days, but they did not arouse suspicion. Curinna Imuhl, 12, who lives near the rented house, said, “I thought no one was there; the shades were always down.”
On Tuesday, the Danish police arrested eight people in a suspected terrorist plot. The German interior minister, Wolfgang Schäuble, said there was no evidence of a direct link between the plots. Six of those suspects have already been released.
Ms. Harms, the federal prosecutor, said the three suspects arrested Tuesday belonged to a German cell of the Islamic Jihad Union, a radical Sunni group based in Central Asia that split from the extremist Islamic Movement of Uzbekistan.
While this group has not been linked to terrorist attacks in Europe, it has claimed responsibility for suicide bombings in July 2004 near the United States and Israeli Embassies in the Uzbek capital, Tashkent. The group has called for the overthrow of the secular government in Uzbekistan.
German officials have warned that the country was under threat of a terrorist attack because of Germany’s involvement in Afghanistan. They said they were particularly worried by reports of Germans taking part in terrorist training camps in Pakistan and returning to Germany to carry out attacks.
In Berlin, Chancellor Merkel said, “The lesson from this is the danger is not just abstract, it’s real.” The consequences of an attack, she added, would have been “indescribable.”
Mr. Ziercke said the United States aided German authorities. Another security official said the Americans tipped off the Germans to the existence of the Islamic Jihad Union.
President Bush, who is in Australia, was briefed on the arrests, said Gordon D. Johndroe, a spokesman for the National Security Council.
American officials, who have spoken publicly about Al Qaeda’s growing abilities to attack Western targets, say the group in Germany is likely to have ties to Al Qaeda’s operational figures in Pakistan. American spy agencies believe that Qaeda’s leaders have established a haven in Pakistan, where they have set up small compounds to train operatives for attacks on Western targets.
American military officials said the Germans contacted them on Tuesday evening to warn them about the plot. “This was a German-led investigation,” said Lt. Cmdr. Corey Barker, a spokesman for the United States European Command in Stuttgart. “We do appreciate their commitment to safeguarding us against a terrorist attack.”
Ramstein is the largest American air base in Germany and a hub for troops deploying to Eastern Europe, Iraq and Afghanistan. Commander Barker said the base had not lifted its force protection level, which is now at the second highest designation.
Frankfurt’s airport, the second busiest on the Continent, after Charles de Gaulle in Paris, was operating normally, an airport spokesman said.
Germany narrowly missed a smaller terrorist attack in July 2006, when two suitcase bombs left on commuter trains in Cologne failed to explode. Officials said the two suspects in that attack, from Lebanon, had a fraction of the bomb-making chemicals amassed for this latest plot.
In June, Mr. Schäuble and his deputy, August Hanning, warned that the terrorist threat was comparable to that in the months before the Sept. 11, 2001, attacks in the United States. That plot was hatched in Hamburg by Islamic militants posing as students.
Mr. Schäuble coupled his warning with a call for stricter anti-terrorism measures. He said he would like the police to be able to conduct surreptitious searches of computers belonging to people suspected of being terrorists.
In the past, some critics here have accused Mr. Schäuble of ratcheting up fears of terrorism in order to build support for his measures. But no such criticisms were voiced on Wednesday.