The US’s ambassador to Germany has been summoned to discuss the possible tapping of Chancellor Angela Merkel’s phone.

German magazine Der Spiegel reported the NSA had been spying on Merkel for years – an allegation German intelligence services have been quoted as saying was plausible.

Germany’s foreign minister has now summoned ambassador John Emerson to discuss the issue.

It comes after Merkel called President Barack Obama to demand immediate clarification over the allegations.

Meanwhile the leader of Germany’s Social Democrats (SPD), Sigmar Gabriel, said it would be hard to imagine agreeing a free trade deal with the United States if the US was infringing citizen’s rights and privacy.

The SPD and Merkel’s conservatives are currently engaged in talks on building a new coalition government.