The German chief prosecutor's office Monday scrapped a controversial treason probe against bloggers that had sparked a wave of press freedom protests.

It said it agreed with the justice ministry that the published papers -- on plans by the domestic spy agency to step up Internet surveillance -- did not constitute "state secrets".

The uproar over Germany's first treason investigation in over half a century, against Netzpolitik.org (Net politics) -- which calls itself a digital civil rights blog -- had led to a major political spat and the sacking of chief prosecutor Harald Range last week.

On Monday his office said in a statement that "the chief federal prosecutor has closed the investigation over suspicion of publicly revealing a state secret."

It said a probe over who leaked the papers, however, would continue and be handed to a local prosecutor's office which would investigate on charges of "violation of professional secrecy".

News of the investigation had sparked protests from journalists, activists and lawmakers who condemned the case as an attack on press freedom and an attempt to intimidate investigative reporters.

Questions of state surveillance, including the NSA scandal revealed by fugitive US intelligence contractor Edward Snowden, are hotly debated in Germany, a country with raw memories of fascist and communist dictatorships.

The charge of treason -- to reveal state secrets to the detriment of the nation and to aid a foreign power -- carries between one year and, in very serious cases, life in jail.

Markus Beckedahl, the founder of Netzpolitik.org, told AFP Monday: "I am not surprised that the investigation has been closed because it was a preposterous legal construct.

"Now we demand transparency on whether we became victims of surveillance measures during the investigation."