Western allies are considering a military strike against Syria as a response to the alleged use of chemical weapons on a suburb of Damascus. U.S. Secretary of State John Kerry last week said more than 1,000 civilians were killed in the attack.
Gerhard Schindler, director of Germany's Federal Intelligence Service, said Berlin had evidence to support U.S. claims that Assad was responsible for the order to use sarin nerve gas during the Aug. 21 strike, German news magazine Der Spiegel reported Tuesday.
He said his intelligence doesn't provide concrete proof the orders came from Assad's regime. Intercepted phone calls between Hezbollah leaders in Lebanon and Iranian officials, however, suggest the Shiite movement was aware of the attacks.
Der Speigel said Hezbollah may have suggested Assad made a mistake by ordering the use of chemical weapons.
Hezbollah this year admitted to fighting alongside Assad supporters during Syria's civil war.
A joint statement from the U.S. and Swedish governments Wednesday said "those responsible for the use of chemical weapons must be held accountable."
The Swedish government said it would work through the United Nations on any response to the crisis in Syria. Germany said it wouldn't take part in any military intervention in Syria unless the full U.N. Security Council backed the move.