Participants at a confidential meeting of German lawmakers said the head of the BND foreign intelligence agency told them it had intercepted a phone call believed to be between a high-ranking member of the Lebanese Shi'ite militant group and the Iranian Embassy in Damascus.
"The BND referred to a phone call they had heard between a Hezbollah official and the Iranian embassy in which he spoke about Assad having ordered the attack," one of the participants told Reuters.
In the phone call, the Hezbollah official says Assad's order for the attack was a mistake and that he was losing his nerve, the participants reported the BND briefing as saying. Both Iran and Hezbollah support Assad.
A BND spokesman declined to comment on Monday's briefing, saying German intelligence speaks only to the government and to parliamentary committees on highly sensitive matters.
A Hezbollah spokesman was not available for comment.
The US goverment says about 1,400 people, hundreds of them children, died near Damascus on August 21 in what it says was a sarin gas attack by the Syrian government.
US President Barack Obama is seeking Congressional backing for taking military action against Assad and Frace has also called for strikes. But British Prime Minister David Cameron failed last week to win parliamentary backing for any action against Syria.
France's military and foreign intelligence services submitted to French lawmakers on Monday a report suggesting that forces loyal to Assad in the country's two-year-old civil war, had carried out the attack.