Dirk Nockemann, the Hamburg senator responsible for internal affairs, said on Tuesday the Islamic group Ansar al-Islam, which is alleged to have links to al-Qaida, was likely behind the plans.
Citing US intelligence sources, he said members of the group had planned a bomb attack on the hospital, while an alternative target was the major US Rhein-Main air base in central Germany.
Security at the hospital was immediately intensified on Tuesday and surrounding streets sealed off.
Aljazeera's correspondent in Germany said "more than 100 German policemen were deployed on Tuesday around the hospital".
"German authorities have also stepped up security measures in almost all public places, fearing attacks on New Year's Eve," added the correspondent from Berlin.
The head of the regional intelligence service, Heino Vahldiek,
said the source of the information was the US Central Intelligence Agency (CIA) and the planned attack was scheduled for the start of 2004.
Vahldiek told local media several people suspected of
involvement in the plot were believed to have already arrived on German soil.
US intelligence officials have passed on the names of two
suspects in particular, whom German authorities are trying to track down, he added.
Police spokesman Reinhard Fallak said US soldiers had been treated in the past at the hospital facility in the Wandsbek suburb of Hamburg, possibly including some who had served in Iraq.
Security at the hospital has been
No US troops are currently at the hospital, another police official said. Fallak said there was no clear evidence on when the attack was planned, but that it involved extremists "from Europe" but outside Hamburg.
In a statement, police said security sources had passed on "concrete evidence about people seeking to attack the hospital with a car bomb. "The potential perpetrators are understood to come from Islamic, terrorist circles."
Fallak said the evidence had been judged by police as "very serious." Streets around the hospital had been closed and would remain so for as long as necessary, added police, who are working in conjunction with the army.
German Interior Minister Otto Schily in a statement noted "unconfirmed indications that attacks had been planned against American military infrastructures in Germany."
"The potential perpetrators are understood to come from Islamic, terrorist circles."
German police statement
"These indications are being checked," he said, adding that the "premature publication" of the information "threatens the success of the investigation."
The military hospital has 305 beds and handles some civilian
services as well as military patients.
German intelligence services believe about 100 Ansar al-Islam
members are present in Germany, mainly in the south of the