Extent of NSA’s spying revealed as Merkel’s phone said to have been tapped for ten years‏

New allegations emerged that US intelligence agencies have been monitoring German Chancellor Angela Merkel’s phone as German officials prepare to travel to the US to seek explanations.

Merkel is said to be furious after Der Spiegel said that her phone had been listed by the National Agency Surveillance (NSA) since 2002 and may have been monitored for more than ten years.

The reports in Germany’s media are based on US intelligence documents leaked by Edward Snowden, a former CIA agent. The leaked documents disclosed classified details of several top-secret mass surveillance programs carried out by the United States to the press earlier this year.

The nature of the monitoring of Mrs Merkel’s mobile phone is not clear from the files as of yet. It is possible that the Chancellor’s conversations were recorded or that her contacts were simply assessed, says the newspaper Der Spiegel.

Another report says Obama was told in 2010 about the surveillance and failed to stop it.

The US president apologised to the German Chancellor and promised Mrs Merkel he knew nothing of the alleged phone monitoring and would have stopped it if he had, Der Spiegel reports.

Ahead of the latest claims, the German government’s deputy spokesman, Georg Streiter, said a high-level delegation was heading to the White House and National Security Agency to “push forward” investigations into earlier surveillance allegations.

The delegation will include senior officials from Germany’s secret service, according to German media reports.

Germany’s Federal Prosecutor’s Office may summon Edward Snowden to be a witness in the case of phone tapping against Angela Merkel, German Justice Minister Sabine Leutheusser-Schnarrenberger told the Deutschlandfunk radio on Sunday.

The spy row has led to the worst diplomatic crisis between the two countries in living memory.

Merkel is said to be shocked that Washington may have engaged in the sort of spying she had to endure growing up in communist East Germany.

Ludovic Caritey