Edward Snowden has endorsed the legitimacy of Wikileaks’ “largest ever” release of sensitive CIA material.

The former CIA systems analyst, who famously leaked classified information from the National Security Agency in 2013, confirmed that the secret files “look authentic”.

“What Wikileaks has here is genuinely a big deal,” Mr Snowden tweeted.

In its first response to the leak the CIA said Americans should be “deeply troubled” by the disclosure.

However the CIA didn’t confirm its files were stolen. CIA spokeswoman Heather Fritz Horniak says the agency will not comment on the authenticity of the documents released or on the status of any investigation into the source of the documents.

The agency says such disclosures not only jeopardise US personnel and operations, but also equip American adversaries with tools and information to damage US national security.

Intelligence and law enforcement officials are still reviewing the cache of more than 8,000 documents released.

More than 8700 documents exposed sophisticated software tools used by the US Central Intelligence Agency to hack into everyday electronic devices.

The files were leaked to the public on Wednesday by Julian Assange’s anti-secrecy group Wikileaks.

Still working through the publication, but what @Wikileaks has here is genuinely a big deal. Looks authentic.

— Edward Snowden (@Snowden) March 7, 2017

White House press secretary Sean Spicer declined to confirm or deny the authenticity of the leaked documents.

“This is the kind of disclosure that undermines our country, our security,” Mr Spicer told reporters on Wednesday.

“This alleged leak should concern every American for its impact on national security.

“Anybody who leaks classified information will be held accountable to the maximum extent of the law.”

The FBI and CIA have launched a federal criminal investigation into the Wikileaks documents, according to Washington Post reports.

Wikileaks did not identify the source of the information, but reported that it was hoped the public dissemination of the files would prompt “public debate about the security, creation, use, proliferation and democratic control of the cyberweapons”.