German officials will visit Tehran on Sunday for talks on Iran's nuclear drive, top Iranian negotiator and deputy foreign minister Abbas Araqchi said on Tuesday.

The meeting will follow similar discussions with American, Russian and French negotiators this week ahead of the resumption of political talks between Iran and the main P5+1 group of world powers on Monday in Vienna.

Germany's foreign minister said Sunday that only "substantial" talks between Moscow and Kiev would help defuse the Ukraine crisis, ahead of an upcoming meeting with his Russian counterpart.

Frank-Walter Steinmeier told a German Sunday newspaper that a resolution was still far off but several developments had given rise to hope, such as the Ukrainian presidential vote, or the first meeting between the Russian and Ukrainian presidents.

A bitter row over the top EU job escalated Thursday after German Chancellor Angela Merkel and British Prime Minister David Cameron had what officials called "candid" talks on the hotly debated issue.

London objects to Merkel's favored candidate to become the next European Commission chief, former Luxembourg premier Jean-Claude Juncker, on the grounds that he supports further political union in the 28-member bloc.

German Chancellor Angela Merkel reiterated a warning Wednesday ahead of a G7 summit that Russia could face new stepped-up economic sanctions if it does not help defuse the crisis in Ukraine.

Hours before the Group of Seven rich countries begins talks in Brussels without Russia, Merkel called in a speech to parliament for stiffer border controls by Russia to stop fighters or weapons crossing into Ukraine.

Germany's federal prosecutor said Wednesday he had opened an investigation over alleged snooping by the U.S. National Security Agency (NSA) on Chancellor 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.

German prosecutors have filed terrorism charges against a Lebanese man accused of belonging to a hard-line Islamic group in Syria, and two suspected accomplices.

Federal prosecutors said Wednesday the main suspect, identified only as Ismail I., was charged with membership in the Islamic State of Iraq and the Levant, an al-Qaida breakaway group.

Inflation in Germany, Europe's biggest economy, it set to slow in May, data showed on Monday, turning up the pressure on the European Central Bank to act and avert deflation, analysts said.

According to closely watched state regional data published so far, German inflation looks set to have slowed in May from the 1.3 percent recorded in April.

German Foreign Minister Frank-Walter Steinmeier said on Saturday that ongoing negotiations between world powers and Iran over its disputed nuclear program have been "encouraging".

His remarks in Abu Dhabi come ahead of a new round of talks in mid-June between Iran and the P5+1 powers of Britain, China, France, Russia, the United States and Germany.

Germany expressed its "dismay" to the Turkish ambassador in Berlin this week over disparaging remarks Prime Minister Recep Tayyip Erdogan made about a German opposition leader, a diplomatic source said Friday.

Amid heightened tensions between Ankara and Berlin, Erdogan complained to deputies from his AKP party on Tuesday that a leader of the German Greens party of Turkish origin, Cem Ozdemir, had said "very ugly things" about him.

Foreign Minister Jebran Bassil on Thursday stressed the need to “take the necessary measures” to address the Syrian refugee crisis in Lebanon and prevent the “collapse” of the country, noting that “Lebanon cannot await the political solution in Syria.”

“We explained the Lebanese strategy in combating international terrorism, especially in light of the Syrian spillover,” Bassil said after talks in Beirut with his German counterpart Frank-Walter Steinmeier.