German media say Angela Merkel's predecessor was put under surveillance after opposition to military action in Iraq in 2002

US intelligence agencies began monitoring the mobile phone of the German chancellor more than 10 years ago when Gerhard Schröder was leader, according to German media.

The Social Democrat chancellor was put under surveillance from around 2002, according to research by newspaper Süddeutsche Zeitung and TV network NDR, reportedly because of his government's opposition to military intervention in Iraq.

Last October the current chancellor, Angela Merkel, accused the National Security Agency of tapping her phone and was later given assurances by the US president, Barack Obama, that the US "is not monitoring and will not monitor the communications of Chancellor Merkel".

It now emerges she was not the first chancellor to have phone calls and text messages monitored, with the NSA said to have collected metadata from Schröder's phone as well.

The source of the latest information is a document leaked by NSA whistleblower Edward Snowden.

The document, containing information about the so-called National Sigint Requirement List, had previously been interpreted as referring only to Merkel's mobile.

But Süddeutsche Zeitung and NDR claim to have confirmation from NSA insiders that the surveillance authorisation pertains not to the individual, but the political post – which in 2002 was still held by Schröder.

"I would never have imagined that I was being bugged by American services then," Schröder said in response to the revelations, "but now I am no longer surprised."

There has been speculation for some time that German politicians other than Merkel have been under NSA surveillance, but the latest revelations seem to confirm these rumours.

Unlike Merkel, who has been an enthusiastic user of her mobile phone since taking office, her predecessor Schröder had an ambivalent relationship with electronic gadgets. In 2005, he claimed in an interview that he didn't have a mobile phone at all: if someone wanted to get hold of him, he said, they would just call his personal assistants who would hand over the phone.

Schröder's former spokesman Béla Anda expressed his surprise via Twitter, saying the former chancellor "didn't have his own phone, but kept on changing it"

Caitlin Hayden, spokeswoman for the Obama administration's national security council, declined to comment on the specific allegations but pointed out that the president has announced a series of reforms to surveillance activities involving foreign targets that would address "significant questions that have been raised overseas". The reforms, announced in a speech last month, would "ensure that we take into

account our security requirements, but also our alliances", she said..

The latest revelations about NSA surveillance of German politicians come as US diplomats are working hard to repair trust. On Tuesday night the US ambassador in Berlin, John B Emerson, had given a talk in front of the Association of Berlin Traders and Industrialists (VBKI), in which he reassured his audience that their concerns "are being taken very seriously at the highest political level" and that listening to the chancellor's mobile "had nothing to do with preventing terrorism".

"We've done a number of stupid things in the US", Emerson said in his speech, "the [monitoring of Merkel's] cell phone being one of them.

"Friends can disappoint one another", the ambassador insisted, "but they work hard to get through it."