German authorities are hunting for about 10 more suspects believed to have helped the three men held for allegedly plotting massive bomb attacks.
A masked officer leads a terror suspect (in blue) to a helicopter
The Islamist plotters were targeting US facilities in Germany, officials said.
The 10 sought are "Germans, Turks and other nationalities," a top security official, August Hanning, told German ARD television on Thursday.
Germany announced on Wednesday that it had arrested two Germans and a Turk suspected of planning huge bombings.
Federal prosecutor Monika Harms said the three had trained at camps in Pakistan and procured some 700kg (1,500lbs) of chemicals for explosives.
She said the accused had sought to target facilities visited by Americans, such as nightclubs, pubs or airports.
Defence Minister Franz Josef Jung said the men had posed "an imminent threat".
Media reports said the men were planning attacks against a US military base in Ramstein and Frankfurt airport.
Ms Harms said the men planned to use vehicles loaded with the explosives to kill or injure large numbers of people.
The arrests had prevented "massive bomb attacks", she said.
The suspects, aged 22, 28 and 29, were alleged to be members of the German cell of a group she named as Islamic Jihad Union.
Two of the men were German nationals who had converted to Islam, while the third was a Turkish man.
Ms Harms said the al-Qaeda-linked group had set up the cell last year.
They were arrested on Tuesday afternoon in a raid on an apartment in North Rhine-Westphalia.
Another 40 raids were been carried out on properties across the country.
Interior Minister Wolfgang Schaeuble called the men "very dangerous terrorists".
"They obviously planned these attacks on the orders of an international network," he said.
Mr Schaeuble said one man was linked to a mosque in the southern city of Neu-Ulm that authorities had suspected for years was an extremist base.
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 has soldiers in Afghanistan but did not send troops to Iraq, has been largely spared terrorist attacks.
Six years ago, the northern city of Hamburg was thrust into the spotlight after it emerged a cell had used it as a base for planning the 11 September 2001 attacks in the US.
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