..."We have a common threat," Schaeuble told reporters. "I am totally convinced that we must not unilaterally decide in all these sensitive regards. We should strengthen international institutions wherever possible."

Schaeuble suggested Monday that Europe and the US "discuss international law issues" related to terrorist threats - for instance, at what point wartime laws take over from peacetime laws.

"Also the distinction between combatant and non-combatant seems to be no longer sufficient," Schaeuble, a member of German Chancellor Angela Merkel's governing centre-right Christian Democrats, said in a speech.

"We have to come to solutions," he said Tuesday. "We have to have a public debate."

Schaeuble confirmed German media reports that investigators believe the bomb detonators seized in a foiled terrorist plot in Germany came from Syria.

Germany this month arrested three alleged Islamic militants accused of planning to blow up car bombs at US military sites and elsewhere in a "massive" terror attack. They were part of a group linked to al-Qaeda and had trained in Pakistan, authorities said.

"We know the fuses for these bombs ... they came from Syria via Turkey to Germany. We don't really know more," Schaueble said.