Three men have been arrested in Germany on suspicion of planning a "massive" terrorist attack on US facilities in the country, officials have said.
Federal prosecutor Monika Harms said the three had trained at camps in Pakistan and procured some 700kg (1,500lbs) of chemicals for explosives.
Defence minister Franz Josef Jung said the men had posed "an imminent threat".
Media reports said they were planning attacks against a US military base in Ramstein and Frankfurt airport.
Ms Harms said the accused - two Germans and one Turkish citizen - were suspected members of the German cell of a group she named as Islamic Jihad Union.
Their arrests had prevented "massive bomb attacks", she said.
Wolfgang Bosbach, an MP with Chancellor Angela Merkel's Christian Democrats, said the suspects had been under observation for a long time.
"We know without any doubt that they were planning attacks that would have had considerable consequences," he told Germany's N24 television, adding that the three had acquired chemicals for the plot.
He said the plot may have been timed to coincide with the anniversary of the September 11, 2001 attacks in the US.
Government sources told the AFP news agency that the three had links to Pakistan and had been experimenting with explosives and trying to build car bombs.
Prosecutors said the arrests took place on Tuesday afternoon.
Frankfurt airport is continental Europe's busiest, and the base at Ramstein in western Germany is a major transport hub for US military operations.
Germany, which did not send troops to Iraq, has been largely spared terrorist attacks, but there have been growing concerns that Islamist militants are operating in the country.
Last summer, two suitcase bombs were planted on commuter trains in several towns but they failed to explode.
On Monday, two people with suspected links to al-Qaeda were arrested in Denmark on suspicion of planning a bomb attack.
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