Germany opens investigation into alleged NSA Merkel phone tap

German prosecutors have opened an investigation into the alleged monitoring of Chancellor Angela Merkel's cellphone by the U.S. National Security Agency, officials said Wednesday, in a move that could again complicate diplomatic relations between the two allies.

It wasn't immediately clear what the new investigation might mean in terms of possible prosecutions of Americans.

Documents provided by NSA leaker Edward Snowden indicated in October the U.S. was monitoring Merkel's cellphone conversations, as well as those of 35 other foreign leaders. Merkel expressed outrage and accused Washington of a grave breach of trust.

In the ensuing diplomatic fallout, President Barack Obama acknowledged Germany's anger and promised that new guidelines would cut back on such monitoring, except in the case of a national security interest.

"The leaders of our close friends and allies deserve to know that if I want to learn what they think about an issue, I will pick up the phone and call them rather than turning to surveillance," Obama said at the time.

Following the news of the German probe, Obama's deputy national security adviser, Ben Rhodes, said the United States believes direct dialogue between the two countries rather than an investigation is the best way to address Germany's concerns.

"We believe we have an open line and good communication" with Merkel and her team, Rhodes told reporters aboard Air Force One as Obama flew to Brussels for a meeting of the Group of Seven nations.

After mulling for months whether to open a formal probe, Chief Federal Prosecutor Harald Range determined "that sufficient factual evidence exists that unknown members of U.S. intelligence services spied on the mobile phone of Chancellor Angela Merkel," his office said.

"The operation of a foreign intelligence service's secret agents is a criminal offense in Germany," Range told reporters after the decision was announced. "And that's not dependent on whether it is the intelligence agency of a friend or of another nation."

Range refused to say how he would interrogate witnesses, saying he couldn't comment on any specifics about the investigation.

In his Wednesday announcement, Range's office said he was not opening a formal investigation of wider allegations of blanket surveillance of telecommunications data in Germany by U.S. and British intelligence, saying that there was not yet sufficient factual evidence of concrete crimes. His office said that would remain under consideration.

In November, citing documents leaked by former NSA contractor Edward Snowden, the Guardian named Germany as a country where intelligence agencies had been working together on mass surveillance programs in cooperation with counterparts including Britain's surveillance agency GCHQ.

Separately, the German Parliament earlier this year set up a committee to investigate the scope of spying by the U.S. and its allies in the "Five Eyes" network — which also includes Britain, Canada, Australia and New Zealand — in Germany.

It is also seeking testimony from Snowden, who currently resides in Russia. Opposition parties want him brought to Berlin to testify, but the government argues that that would hurt trans-Atlantic relations and security cooperation with the U.S.

Al Jazeera and wire services