Germany has arrested three men it suspects of belonging to an Islamist terrorist group and planning attacks on Frankfurt international airport and a major U.S. military base, German officials said on Wednesday.
Defence Minister Franz Josef Jung told German television that the three had planned to launch attacks soon and described the plot as "very concrete".
"There was an imminent security threat," Jung said.
The arrests come a day after Danish police conducted raids and took eight young Muslims into custody whom they suspect of plotting a bomb attack and having links to al Qaeda.
They also occurred less than a week before the sixth anniversary of the Sept. 11 2001 hijacked plane attacks on targets in the United States.
The Federal Prosecutor's Office in Karlsruhe, which was to hold a news conference later on Wednesday, said that raids had been carried out in several German states on Tuesday.
"The German federal prosecutors office ordered the arrest yesterday afternoon of three suspected members of an Islamic terrorist organization," it said in a statement.
A German security source told Reuters that the plotters had obtained chemicals and detonators that could have led to an attack on the scale of those in Madrid and London in past years, which killed 191 and 52 people respectively.
The source said the three men included two German nationals that had converted to Islam and one Turkish man. All three had trained in militant camps in Pakistan, the source added.
"There is hard evidence that the suspects were targeting Frankfurt airport and the U.S. base in Ramstein," the source said, noting that the suspects had been under surveillance for months and that one had been observed scouting out Ramstein.
Hub for Afghanistan, Iraq
Frankfurt airport is one of Europe's busiest and a major international hub with about 52 million passengers and 2 million metric tonnes of cargo passing through it each year.
The Ramstein base in the nearby state of Rhineland-Palatinate, 130 km (80 miles) southwest of the airport, is one of the most important U.S. air bases overseas and is a hub for U.S. operations in Afghanistan and Iraq.
A spokesman for the airport declined comment. Captain Jeff Gradeck, a spokesman for the U.S. European Command (EUCOM) in Stuttgart, said: "We don't have any information yet that U.S. facilities were targeted."
Germany, which has forces stationed in Afghanistan, has been on high alert for attacks. The country has feared a re-emergence of militant Islamic groups since 2001, when the northern city of Hamburg was used as a base for planning the Sept. 11 attacks.
In April the U.S. embassy in Berlin announced it was boosting security at diplomatic and military facilities in Germany in response to an increased threat of terrorism there.
Last year, two men of Lebanese origin attempted to detonate crude suitcase bombs on two trains in Germany, according to German authorities. Prosecutors have said the bombs failed to go off because of a technical error.
EU Justice and Security Commissioner Franco Frattini, speaking in Strasbourg, said the arrests in Germany and Denmark proved the fight against terrorism was achieving results in Europe but cautioned that the threat of attacks remained high.
"All sources indicate that the threat of new terrorist attacks continues to be high," Frattini said.