BERLIN, Germany (CNN) -- German authorities are tracking a list of people believed to have a connection to a foiled terror plot against American military installations and other Western targets in Germany, according to prosecutor and Interior Ministry officials.
German authorities know the whereabouts of all the people who are in Germany, Frank Wallenta, of the federal prosecutor's office said Friday but he refused to elaborate on the exact number of those remaining in that country.
Police have not taken them into custody because there is insufficient evidence to arrest them, he said.
The people are still at large and are of various nationalities -- some living in Germany and some outside the country, Interior Ministry spokesman Christian Sachs.
On Thursday an interior ministry spokesman said police were searching for 10 suspects believed to have belonged to the terror network that provided assistance to the three men accused in the plot.
German authorities announced Wednesday they had arrested three men -- two Germans and one Turk -- as they started mixing a massive amount of explosive materials that could have resulted in a stronger explosion than the terror attacks in Madrid in 2004 and London in 2005. Watch a report on the three arrests ยป
The suspects also possessed several sophisticated detonators, picked up during a series of raids on Tuesday, that had been brought to Germany in "conspirative" way, Sachs said.
The detonators were the type that can be used in a military device, which are difficult to obtain, more precise and can inflict more casualties than lower-grade detonators, according to a counterterrorism source in Frankfurt with knowledge of the plot.
The two German suspects in custody -- both converts to Islam -- were identified by German media as Fritz Gelowisc, 28, and Daniel S., 22; the Turkish man was identified as Adem Y., 29.
According to the reports, Gelowisc was a leading member of a radical Islamist center in Ulm in southern Germany and was well known to German authorities.
The three men were arrested Tuesday during a raid on a rental house in west-central Germany.
Sachs said investigators are also analyzing evidence -- including computer hard drives -- picked up during that raid and the others that followed Tuesday's arrests.
German Interior Minister Wolfgang Schaeuble said there were strong grounds for believing that the trio were planning attacks against U.S. military facilities in Germany.
German media has named the Ramstein Air Base -- the U.S. military's primary site in Germany -- and Frankfurt's international airport as possible targets.
Schaeuble said he had "no knowledge of any link" with the arrests in Denmark on Tuesday of eight suspected Islamic militants accused of storing explosives in a populated area of Copenhagen with the intent of carrying out a terror attack.
The U.S. was "closely monitoring" the arrests in Germany and Denmark, Department of Homeland Security spokesman Russ Knocke told CNN.
"At this time, there is no credible information telling us of an imminent threat to the homeland, but we do believe that we continue to be in a period of increased risk," he said.
A U.S. counterterrorism official told CNN the the German terror plot was "the real deal," adding that U.S. authorities had been involved since the "earliest stages of the investigation."
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Possible Targets
Ramstein
Headquarters of U.S. Air Forces in Europe
Key stop for troops and supplies on way to Afghanistan and Iraq
Nearby is Landstuhl Regional Medical Center, used to treat wounded troops
Frankfurt Airport
More than 50 million passengers each year
Key airline hub
About 1,300 flights per day
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What is so scary about this is I flew into the Frankfurt airport last week...
