Iran has allowed Syria's regime to station fighter jets on its territory to keep them safe from foreign attack, German intelligence services believe according to a media report Sunday.

News portal Spiegel Online said the report, marked "classified", pointed to close military ties between Damascus and Tehran beyond the deployment of Iran-backed Hezbollah militia on the side of regime forces.

The German intelligence paper reportedly said Iran had also sent elite troops from its Revolutionary Guard to support the forces of Syrian President Bashar al-Assad.

The intelligence report also said a source had reported that a Syria-Iran military deal from November 2012 allowed Assad "to station large parts of his air force on safe Iranian territory and to use them when needed," said Spiegel Online.

The weekly news magazine Spiegel, meanwhile, published an interview with Assad in which he again denied responsibility for deadly chemical weapons attacks in late August, accusing rebels whom he labels terrorists of being behind them.

"We have not used chemical weapons. This is wrong," Assad is quoted as saying. "And so is the picture you're drawing of me of someone who kills his own people."

Assad also suggested Germany could play a mediator role in ending the bloody conflict that has killed more than 100,000 people in over two years.

Germany's outgoing Foreign Minister Guido Westerwelle, during an Afghanistan visit, rejected the idea, saying Berlin supports UN special envoy Lakhdar Brahimi, Spiegel Online reported.