Whistleblowing website WikiLeaks has released a 90GB-sized trove of data relating to the ongoing German parliamentary inquiry into the relationship between the county's foreign intelligence agency – the Bundesnachrichtendienst (BND) – and the National Security Agency (NSA).

According to WikiLeaks, the disclosure consists of 2,420 documents from "various agencies" of the German government submitted as exhibits to the inquiry last year. The probe was set up after the Edward Snowden revelations in 2013 which exposed close surveillance links between the agencies.

The leak reportedly includes 125 documents from the BND, 33 from the Bundesamt für Verfassungsschutz (BfV) and 72 from the Federal Office for Information Security (BSI), and more. In a release, WikiLeaks said it features "admin documents, correspondence, agreements and press reactions."

Some individual documents highlighted by the whistleblowing organisation include alleged spying agreements between the BND and the NSA, a file on how a German agency staffer was tasked with contributing to the XKeyscore spy programme.

"The collection offers a detailed insight, not just into the agencies themselves, but the mechanics of the inquiry," Wikileaks said in a release, adding: "Whilst a number of facts have already come to light as a result of the inquiry – including WikiLeaks publication of inquiry transcripts last year – this substantial new collection of primary source documents provides significant new evidence."

Julian Assange, founder of WikiLeaks, said: "Germany cannot take a leadership role within the EU if its own parliamentary processes are subservient to the wishes of a non EU state." He also blasted the "cowardly" stance of the German government over its decision to contest a court ruling which said Snowden should be allowed to testify to the inquiry in person.

"The outrage that was sparked by the Snowden NSA revelations led to the establishment of the inquiry, which later called for Mr Snowden to testify at it," he said. "This substantial body of evidence proves that the inquiry has been using documents from Mr Snowden and yet it has been too cowardly to permit him to testify."

In a previous release in 2015, WikiLeaks published documents that suggested the communications of over 120 top German government officials, including Chancellor Angela Merkel, were being intercepted by the NSA. The files showed how the surveillance operation had been active for years.

The BND leak comes after WikiLeaks released 'The Yemen Files' – 500 internal documents allegedly from the United States embassy in Sana'a that appeared to show a the close relationship between the US military and Yemeni forces just prior to the devastating civil war breaking out in 2015.

The organisation repeatedly hit the headlines this year after a number of leaks focused on the US political system. In the months leading up to the 2016 presidential election, it disclosed nearly 20,000 emails from a Democratic Party group and thousands of emails from the personal inbox of John Podesta, a close aide to Hillary Clinton.

The backlash following those publications led to the US intelligence community officially accusing it of working with Russian intelligence. Assange – who currently lives under political asylum in London – has denied all links with the Putin-led government.

On 1 December WikiLeaks' website suffered a four-hour outage which led some to speculate it had come under cyberattack. Explaining the downtime, just prior to the release of the BND files, a spokesperson told IBTimes UK: "DDoS attacks probably related a significant intelligence agency publication this afternoon."