It added that US President Barack Obama told the German leader that he would have stopped the eavesdropping had he known about it.
Revelations that Merkel's phone was being tracked by the US National Security Agency (NSA) have sparked an outcry in Germany, and prompted the government to summon the US ambassador. German intelligence officials were to travel to Washington to meet with their US counterparts in the coming weeks, the governments said Friday.
Der Spiegel said Merkel's mobile phone number appeared under "GE Chancellor Merkel" on documents of the NSA's Special Collection Service.
It said the Special Collection Service was operating a "not legally registered espionage branch" at the US embassy in Berlin, where highly advanced equipment was being used to spy on the German government.
Based on a secret 2010 document, the magazine added that the NSA was operating similar spying centres in some 80 location worldwide, including 19 in Europe. It named Paris, Madrid, Rome, Prague, Geneva and Frankfurt as homes to such NSA branches.
The German government said on Friday that Merkel's calls were safe given she normally uses encrypted phones.//DPA