Berlin (AFP) - Germany on Friday announced new measures to curb the activities of its foreign intelligence agency after a damning official report revealed improper collusion with the US National Security Agency.

Berlin will in future implement stricter guidelines governing cooperation between the BND foreign intelligence service and the NSA, deputy government spokeswoman Christiane Wirtz said in a statement.

Oversight of the spy agency directly from Chancellor Angela Merkel's office will also be beefed up, and a list of duties the BND carries out for the NSA will be overhauled.

The steps came after a special investigator appointed by the German government handed over his final report into claims that the BND spied on its European allies for the NSA.

Wirtz said the findings revealed "technical and organisational deficits in the area of strategic surveillance" by the BND.

However, she said "there are no indications of mass spying on German and European citizens".

The report by investigator Kurt Graulich, a copy of which was obtained by AFP, found the NSA had kept a long list of European government offices as targets for espionage and that the United States had thus "clearly violated treaty agreements".

Graulich's 300-page report was based on a review of telephone numbers and IP addresses the NSA handed to the BND's surveillance apparatus with the request that the results to be sent back to the United States.

The findings indicated that over the years the BND whittled down the list of thousands of NSA targets while still maintaining cooperation.

Germany had reacted with outrage when information leaked by former NSA contractor Edward Snowden revealed in 2013 that US agents were carrying out widespread tapping worldwide.

Merkel, who grew up in communist East Germany where state spying on citizens was rampant, declared repeatedly that "spying among friends is not on" while acknowledging Germany's reliance on the US in security matters.

Earlier this year, the BND came under fire over claims it had carried out surveillance of European allies on behalf of the NSA.