New reports published in German media are raising new questions about the extent of U.S. surveillance of Chancellor Angela Merkel. The respected German online and print magazine, Der Spiegel, reports that the National Security Agency had been spying on the German leader since as early as 2002 – and that President Obama, told about the surveillance in 2010, did nothing to stop it. “Obama did not halt the operation but rather let it continue,” an NSA official was quoted saying in the newspaper. Leaked documents to the news source claim that a U.S. listening unit was based in its embassy in Berlin.

The row over alleged spying has lead to the worst diplomatic crisis between the two countries in living memory, the BBC reported. The German Interior Minister Hans-Peer Friedrich said that, should the operation be confirmed, it would be illegal: “If the Americans intercepted cellphones in Germany, they broke German law on German soil.” He added wiretapping is a crime and “those responsible must be held accountable,” according to German newspaper Bild am Sonntag.

The fact that Merkel was spied on three years before she became chancellor indicated that there might have been bugging of the phones of other prominent people in the country, said BBC’s Stephen Evans.

The nature of the monitoring is not clear from the files – whether the conversations were recorded or her contacts simply assessed it is not clear from the files, Der Spiegel says.

Obama apologized to Merkel and promised her he knew nothing of the alleged phone monitoring. However, Bild am Sonntag quoted several U.S. intelligence sources as saying NSA head Keith Alexander personally briefed the President about the covert operation three years ago.

Germany will send its top intelligence chiefs to Washington next week to start an investigation on the spying allegations. The report claims that there were 80 other listening units in locations worldwide, 19 of them in European cities.

Merkel is said to be shocked that Washington may have engaged in the sort of behavior she had to endure growing up in Communist East Germany, the BBC reports.