Three militants from an Islamic group linked to al-Qaida were planning "massive" bomb attacks against Americans in Germany when an elite antiterrorist unit raided their small-town hideout after months of police surveillance, officials said. Prosecutors said Wednesday that the suspects - two German converts and a Turkish citizen sharing a "profound hatred of US citizens" - had military-style detonators and enough material to make bombs more powerful than those that killed 191 people in Madrid in 2004 and 52 commuters in London two years ago. German Federal Prosecutor Monika Harms said the suspects arrested Tuesday were aiming at institutions and establishments frequented by Americans in Germany, including discos, pubs and airports. Her office said the plan was to set off car bombs. "We were able to succeed in recognizing and preventing the most serious and massive bombings," Harms said at a news conference. She declined to name specific targets. In Washington, a senior US State Department official said German investigators had determined the Frankfurt International Airport and the nearby US Ramstein Air Base were the primary targets of the plot, but that those arrested may have also been considering strikes on other sites, particularly facilities associated with the United States. The official spoke on condition of anonymity to describe discussions between American and German intelligence agencies. Germany's announcement was the second in two days that a major attack had been foiled in Europe, after Danish authorities arrested eight alleged Islamic militants with links to senior al-Qaida terrorists. The German raids were launched after an intense, six-month investigation by 300 officers, who followed the suspects so closely that, at one point, police stealthily substituted a harmless substitute for the raw bomb material the suspects had collected, according to prosecutors. German and US officials have been increasingly on edge after Islamist attacks on German troops in Afghanistan, fearing an attack at home, and security measures had been increased. Officials praised law enforcement officers after the raids, but warned that the country could not let down its guard. Chancellor Angela Merkel thanked security officials for foiling the attack, and called the arrests a "very, very great success." "This shows that terrorist dangers, in our country as well, are not abstract but are real," she said. Germany's elite GSG-9 anti-terrorist unit arrested two of the suspects Tuesday at a vacation home in Oberschledorn, a town of some 900 people in central Germany. A third suspect fled through a bathroom window, but was caught about 300 meters away, authorities said. The suspects were brought before a judge in closed-door sessions Wednesday at the Federal Court of Justice in Karlsruhe, and were ordered held pending trial. Prosecutors said the three - whom they identified only as Fritz Martin G., 28, Adem Y., 28, and Daniel Martin S., 21 - had first come to the attention of law enforcement when one or more of them carried out surveillance of US military facilities in Hanau, near Frankfurt, in late 2006. During the first part of the year, they acquired 12 containers of 35 percent hydrogen peroxide solution, which officials said can easily be combined with other material to make explosives. As a token of the intense surveillance by German police, prosecutors said that during the investigation they were able to replace the dangerous peroxide in the containers with a harmless solution without the knowledge of the suspects. The containers were first kept in a garage in the Black Forest region in southern Germany. Subsequently, one of the three rented a vacation cottage in Oberschledorn under a false name on Aug. 17. On Sept. 2, the two other suspects joined him there with the intention, officials said, of making bombs using detonators and electrical components they had obtained. Police decided to move in when the suspects moved one of the containers to the cottage, fearing an attack could be in the offing. The more than 700 kilograms of peroxide could have made a bomb with the explosive power of some 550 kilograms of dynamite. "This would have enabled them to make bombs with more explosive power than the ones used in the London and Madrid bombings," Joerg Ziercke, head of the Federal Crime Office, Germany's equivalent of the FBI, said at the news conference. The use of hydrogen peroxide is by no means a first. The four suicide bombers who killed 52 commuters on three subway cars and a bus in July 2005 in London used bombs made using hydrogen peroxide, which in diluted form is commonly used in hair coloring and as a disinfectant. Officials seized computers and were trying to find out who had offered financial support. Police also searched an Islamic information center in the southern town of Ulm, home to one of the suspects. Prosecutors said the three had undergone training at camps in Pakistan run by the Islamic Jihad Union, and had formed a German cell of the al-Qaida-influenced group. They described the Islamic Jihad Union as a Sunni Muslim group based in Central Asia that was an offshoot of the Islamic Movement of Uzbekistan, an extremist group with origins in that country. "This group distinguishes itself through its profound hatred of US citizens," Ziercke said. The three had no steady work and were collecting unemployment benefits while their main occupation was the plot, officials said. US National Security Council spokesman Gordon Johndroe said in Washington that President George W. Bush was pleased a potential attack was thwarted and appreciated the work of the German authorities. FBI spokesman Richard Kolko said the FBI and US Department of Homeland Security saw "no imminent threat to the US domestically following these arrests." The arrests were another alarming report following a failed train bombing last year and warnings that Germany's troop deployment in Afghanistan could make it vulnerable. German and US officials have warned of the possibility of a terrorist attack. In July 2006, two gas bombs were placed on German commuter trains but did not explode. Officials said that attack was motivated by anger over cartoons portraying the Prophet Muhammad in a Danish newspaper. Several suspects are on trial in Lebanon, and a Lebanese man has been charged in Germany. Additionally, three of the four suicide pilots involved in the Sept. 11, 2001, terror attacks, once lived and studied in Hamburg. Wolfgang Bosbach, a top legislator from Merkel's Christian Democrats, noted the upcoming sixth anniversary of the Sept. 11 terror attacks, as well as deliberations by the German parliament in the next few weeks over whether to extend its troop mandates in Afghanistan. "We are in a highly sensitive period," he said.