German police arrested three men under suspicion of Islamist terrorist group affiliation.

The group was suspected of planning attacks on Frankfurt International Airport and a major US military base.

Defense Minister Franz Josef Jung told German television that the three had been planning to launch the attacks on their targets soon. "There was an imminent security threat," Jung said, adding it was “very concrete.”

“The security services have done a very good job and I can't say anything more at this point.”

In a statement ahead of a news conference planned for 5 a.m. EDT on Wednesday, the Federal Prosecutor's Office in Karlsruhe said raids had been carried out in several German states.

Reports said that two of the suspects were German while the third was Pakistani.

Frankfurt Airport is continental Europe's busiest airport, 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, multiple 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.