Following widespread speculation that the move was imminent, German Federal Prosecutor Harald Range on Wednesday announced he is launching a formal investigation into allegations that the NSA spied on Chancellor Angela Merkel's mobile telephone communications.

SPIEGEL had reported on Monday that the federal prosecutor was close to opening formal proceedings. On Wednesday, Range informed the Legal Committee of the Bundestag, Germany's federal parliament, of the pending investigation.

The move marks the next significant chapter in the spying scandal surrounding America's signals intelligence authority, the National Security Agency. It is also the first formal act taken by a German government agency in response to the revelations made public by NSA whistleblower Edward Snowden. The probe could further exacerbate trans-Atlantic relations that have been deeply burdened by the scandal.

The Federal Prosecutor's Office in Karlsruhe opened two "monitoring processes" last year to review the allegations. The first focused on the mass spying of Germans' data by the NSA and the second targeted allegations -- first reported by SPIEGEL in October -- that Merkel's mobile phone had been tapped.

Germany's federal prosecutor has opened an investigation over alleged snooping by the US National Security Agency (NSA) on Angela Merkel's mobile phone.

"I informed parliament's legal affairs committee that I have started a preliminary investigation over tapping of a mobile phone of the chancellor," Harald Range said.

The long-anticipated inquiry, which follows allegations last year that US spies had eavesdropped on the German chancellor's mobile in the past, is against unnamed persons, Range said after addressing the committee.

However, he said he had decided against opening an investigation into claims of wider NSA surveillance against German citizens.

BERLIN -- German federal prosecutors have opened an investigation into the alleged monitoring of Chancellor Angela Merkel's cell phone by the U.S. National Security Agency, they said Wednesday.

Chief Prosecutor Harald Range has been mulling for months whether to open a formal probe of the Merkel allegations that emerged in October. The revelations cooled relations between Berlin and Washington, prompting Merkel to accuse the U.S. of a grave breach of trust and President Barack Obama to pledge he would not allow America's massive communications surveillance capability to damage relations with Germany or other close allies.

Range's office said he opened an investigation Tuesday into persons unknown regarding Merkel's phone, a move that could again complicate matters diplomatically.

"Extensive preliminary investigations have established that sufficient factual evidence exists that unknown members of U.S. intelligence services spied on the mobile phone of Chancellor Angela Merkel," Range's office said.