Germany is dropping a probe into the alleged tapping of Chancellor Angela Merkel's mobile phone by U.S. spies, due to a lack of evidence, magazine Focus said Saturday.

Six months after the investigation began, the experts have failed to find any solid proof to back the case, and have therefore recommended that it be dropped, the magazine reported, quoting sources close to the German justice ministry.

World powers and Iran have still made no real progress in negotiations over Tehran's nuclear program and it looks "physically impossible" to strike a comprehensive deal by Monday's deadline, a European source said Saturday.

The source close to the negotiations said "no significant progress" has been achieved until now and "there is even a chance that we will not" reach an agreement by Monday's deadline.

Hundreds of Germans have left their home country to fight alongside jihadists in Syria and Iraq, Interior Minister Thomas de Maiziere said.

"We estimate 550. Just a few days ago we had 450," the minister told German television channel Phoenix on Friday.

A Russian spy, jailed in Germany with her husband last year, has been freed early and allowed to return home, media reports said Friday, suggesting a possible prisoner swap.

The 48-year-old woman, known only by the pseudonym Heidrun Anschlag, was freed two days ago and returned to Russia while her 53-year-old husband, known as Andreas, remains in detention, the DPA news agency and Focus magazine reported.

Germany, the third biggest supplier of international troops to Afghanistan, voted Wednesday to extend the deployment's mandate until the end of 2015.

Chancellor Angela Merkel's cabinet agreed to allow up to 850 soldiers to serve in the country for another year.

German Foreign Minister Frank-Walter Steinmeier said Tuesday he was not optimistic about an end to the crisis in Ukraine because of a "dangerous" escalation of fighting in the east.

"There are no grounds for optimism in the current situation," Steinmeier said at a press conference after talks with his Russian counterpart Sergei Lavrov in Moscow, following a visit to Ukraine earlier.

German Chancellor Angela Merkel on Monday called on the West not to lose hope in what may be a long struggle with Russia over Ukraine, but vowed that the Kremlin "will not prevail".

Russia's annexation of Crimea in March "called the whole of the European peaceful order into question, and it has continued by Russia exporting its influence to destabilize eastern Ukraine," Merkel said after attending the G20 summit in Brisbane.

Russian President Vladimir Putin on Sunday shrugged off a hail of Western fire over the Ukraine crisis as G20 leaders wrapped up an annual summit focused on a drive to overhaul the global economy. 

At the summit in Brisbane, Putin broke protocol by delivering remarks to the media before the host leader's closing news conference, and then flew out a little early. 

Britain will walk away from negotiations with European Union partners if its pleas for immigration reform are ignored, raising the real possibility of leaving the bloc altogether, Foreign Secretary Philip Hammond said Friday.

Hammond told the Daily Telegraph that the British public could vote to end the country's membership unless there was "substantial, meaningful reform" from Brussels.

Germany's foreign minister will travel to Israel and the Palestinian territories at the weekend for talks with leaders on both sides amid surging tensions, a spokesman said Friday.

Frank-Walter Steinmeier aims to get a first-hand picture after recent clashes between Palestinians and Israeli forces, a situation in which the "peace process isn't really advancing", the spokesman told reporters.