Al Jazeera's internal communications were hacked by United States spies, German news magazine Der Spiegel has said, citing leaked documents it has seen.

The US National Intelligence Agency accessed Al Jazeera's protected internal systems during President George Bush’s second term in office, Spiegel said.

It also said that the documents were passed to the magazine by US whistleblower Edward Snowden.

"The encrypted information was forwarded to the responsible NSA departments for further analysis, according to the document, which did not reveal to what extent the intelligence agency spied on journalists or managers of the media company, or whether the surveillance is ongoing,” Spiegel added.

Accessing "Al Jazeera broadcasting internal communication" was listed as a "notable success", the document showed, according to Spiegel.

The NSA named Al Jazeera as one of the selected targets and had "high potential as sources of intelligence", the magazine said.

Snowden, a former contracted NSA employee, has been wanted by the US since June for leaking NSA surveillance secrets to the media.

Last month, Snowden was granted temporary asylum in Russia for a year.