"We are part of the global threat by Islamist terrorism," Schäuble told Die Welt am Sonntag newspaper.

The interior minister referred to the abduction in Baghdad in early February of a German woman and her German-Iraqi son days after a second ultimatum by the hostage-takers had run out.

"We are concerned that terrorists are attacking our involvement in Afghanistan with the abduction of two Germans in Iraq," Schäuble said.

The hostage takers have twice set deadlines for Germany to withdraw its 3,000 troops from Afghanistan, posting videos on the Internet of 61-year-old Hannelore Krause Kadhim begging for help with her 20-year-old son Sinana at her side.

Schäuble said attacks on Germany could follow.

"The danger level is high," he said.

Mixed feelings about mission

German officials in a foreign ministry crisis team working to release the hostages have said they have not given up hope, but are "greatly concerned."

According to recent opinion polls, the German public remains broadly behind the country's reconstruction mission in relatively peaceful northern Afghanistan, but there is strong opposition to the deployment this month of six reconnaissance jets to assist NATO forces fighting the Taliban in the south.