Calling 43-year-old Susanne Osthoff's kidnapping a warning for all of Germany, Interior Minister Wolfgang Schäuble told Die Welt newspaper Wednesday the case shows that "we in Germany are also threatened by international terrorism."

The abduction is the first political test for new German Chancellor Angela Merkel's government, which was sworn into office last week. That's a fact the kidnappers were well aware of, according to Kai Hirschmann, deputy director of the Institute for Terrorism Research in Essen.

"The timing of the kidnapping is no accident," he told the Münchner Merkur newspaper Wednesday. "The terrorists wanted to send a clear message to Berlin."

In a video released earlier this week, the kidnappers said they would kill Osthoff and her driver, who was also abducted, if Germany did not end its cooperation with the Iraqi government.

US offers assistance

Calling for the hostages' immediate release, Merkel has vowed to do everything within her power to save them.

After a visit with US Secretary of State Condoleezza Rice, German Foreign Minister Frank-Walter Steinmeier said the US had pledged to help locate Osthoff.

Even though "civil negotiations" would not be possible, Ruprecht Polenz, head of the Bundestag's Foreign Relations Committee, told the Berliner Zeitung that the German government needs speak with the kidnappers and should not rule out paying ransom.

Four others also kidnapped

In addition to Osthoff and her driver, two Canadians, a Briton and an American were also kidnapped in a separate incident on Saturday. A previously unknown group calling itself "The Brigades of the Swords of Righteousness" claimed responsibility for the kidnappings.

More than 200 foreigners have been seized since the US-led invasion in 2003 and around 50 have been executed since 2004.