BND President Gerhard Schindler told a parliamentary committee looking into the allegations that although errors had been made, Germany security depended on his agency's cooperation with the US National Security Agency.

"The NSA is our partner, not our opponent," Schindler told the members of the Bundestag committee on Thursday. He also said that any attempt to end cooperation between the two organizations would hamper the BND's efforts to protect Germany from terrorist attacks.

"We are dependent on the NSA, not the other way around," Schindler said, adding that the Americans had provided the BND with significant information and warnings about terrorist activities, technology and know-how in recent years.

Spot-checks on 'selectors'

Where the German agency erred he said, was in failing to properly vet the list of "selectors" or search criteria that the NSA had asked it to use in surveillance activities conducted from the BND's facility at Bad Aibling in the south of the country. Selectors can include things such as names, telephone numbers or Internet Protocol (IP) addresses.

The Bad Aibling facility was meant to gather data coming out of places like Somalia and Afghanistan, but in recent weeks it came to light that some of these selectors provided by the NSA helped it spy on European companies and officials.

Schindler said the problem was that the BND had initially only conducted spot-checks on the selectors and that the first comprehensive check didn't take place until August 2013. He said that while some spot-checks had indicated that there may be a problem in 2010 and 2011, the information had not been passed on the top levels of the BND's management. Schindler didn't join the BND until 2012. He also said that he had only learned of the problematic selectors discovered in 2013 many months after the fact.

Snowden revelations

The NSA has been widely criticized in Germany since revelations leaked by its former contractor, Edward Snowden in 2013 showed some of the extend of the US agency's activities, including tapping into Chancellor Angela Merkel's phone.

However, Schindler warned that the scrutiny that the BND was coming under, particularly since the most recent revelations was having a negative impact on its ability to gather intelligence, and that several allied agencies were already reviewing their cooperation deals with the BND.

"These developments cause me great worry, as they will ultimately call into question the ability of this service to function in the future," he told lawmakers. "We cannot do our job without international cooperation."

pfd/bw (dpa, AFP)