Germany's spy agency is working again with Syrian President Bashar al-Assad's secret service to swap information on Daesh terrorists, the Bild daily said, despite Berlin's opposition to Assad staying in power under any peace deal in Syria.

Citing well-informed sources, the mass-circulation newspaper said German foreign intelligence BND agents had been travelling regularly to Damascus for some time for consultations with Syrian colleagues.

Two weeks ago Germany's parliament approved a plan to support a U.S.-led air strike campaign against Daesh in Syria by sending Tornado reconnaissance jets, a frigate to help protect the French aircraft carrier Charles de Gaulle, refueling aircraft and up to 1,200 military personnel.

German media have dubbed the mission Chancellor Angela Merkel's "first war" and have highlighted the risks of German pilots crashing in Daesh-held territory.

The aim of renewed BND contacts with Damascus is to exchange information about Daesh terrorists and to set up a fixed communication channel in case a German Tornado pilot is downed over Syria, Bild said.

The BND did not immediately respond to a request for comment.

Bild said the BND wants to open a station in Damascus as soon as possible to have agents permanently stationed there and is making preparations with the government's knowledge.

Agents could potentially move into the German embassy, which is currently closed, Bild reported, and Merkel's government wanted to make a final decision at the start of next year.

Germany's defence minister has ruled out any cooperation between German forces due to take part in the military campaign against Daesh and Assad's forces.

On Wednesday, Merkel told lawmakers in the Bundestag (lower house of parliament) that diplomatic efforts to end the four-year-old conflict in Syria were striving to reach a long-term solution that does not involve Assad.