Tipped by U.S. authorities, German police arrested a Turkish man and his American fiancee for allegedly plotting to attack U.S. military bases in Heidelberg on the anniversary of the Sept. 11 terror attacks, German authorities said Friday.

Authorities on Thursday found 287 pounds of chemicals and five pipe bombs along with a picture of Osama bin Laden in the couple's apartment near Heidelberg, home to the U.S. Army Europe headquarters.

"We suspect that they intended to mount a bomb attack against military installations and the city of Heidelberg," the chief law enforcement officer for Baden-Wuerttemberg state, Thomas Schaeuble, told reporters.

Authorities were looking into whether the couple was acting alone or were part of a network. However, federal authorities investigating the Hamburg terror cell that participated in the Sept. 11 attacks on Washington and New York have left the new case in the hands of state officials, giving an indication that the plans appeared isolated.

The 25-year-old Turkish man and his 23-year-old fiancee both indicated a hatred for Jews, Schaeuble said. Neither were identified, but U.S. officials in Washington said the woman had dual U.S. and Turkish citizenship.

Their occupations would have given both the access necessary to carry out the planned attack, Schaeuble indicated. The man worked in a chemical warehouse in nearby Karlsruhe. The woman worked in a supermarket at a U.S. installation in Heidelberg, where some 16,000 American soldiers, family members and civilian workers are stationed.

There were no signs of heightened alert at the Campbell Barracks in Heidelberg Friday evening. Joggers ran past the fenced-in headquarters and children played outside at military housing across the street.

U.S. Army Europe spokesman Sandy Goss said he had no details about a possible target.

"All I know is there were two people arrested and we're monitoring the situation closely because we take all these reports seriously," Goss said.

Earlier this week, federal Interior Minister Otto Schily said German authorities had no information on planned attacks around the anniversary of the Sept. 11 attacks and that 500 tips indicating potential threats since last year's attacks were not well-founded.

In a separate incident, federal prosecutors said Friday they are investigating a 39-year-old Afghan-born man who lived in Hamburg and holds a German passport for possible terror links. The man was arrested by U.S. authorities after he traveled to the United States in mid-July, and was in custody in Alexandria, Virginia.

Federal investigators started their investigation on Aug. 20, a spokesman for federal prosecutors, Hartmut Schneider, said. He refused to give further details.

Three of the suicide pilots in the Sept. 11 terror attacks in the United States belonged to a Hamburg terror cell, living seemingly normal lives as students while they nurtured plans to attack the United States.

Federal prosecutors said they believe that while the Hamburg cell carried out the plot, it was conceived elsewhere in the al-Qaida network. Members of the cell traveled to Afghanistan in November 2000, prosecutors said, where it is believed they received training and financial support.

Only one alleged member of the cell has been arrested, 28-year-old Mounir El Motassadeq, a Moroccan accused of helping the cell with logistics. An indictment issued last week charges him with belonging to a terror group and some 3,000 counts of being an accessory to murder. Trial is to begin this fall in Hamburg.

German authorities have issued international arrest warrants for three other suspected members of the cell who disappeared before the attacks.