BERLIN: US President Barack Obama was personally informed of phone tapping against German Chancellor Angela Merkel which may have begun as early as 2002, according to media reports stoking anger over a spiraling espionage scandal.

Bild Sonntag newspaper quoted US intelligence sources as saying that National Security Agency chief Keith Alexander had briefed Obama on the operation against Merkel in 2010. “Obama did not halt the operation but rather let it continue,” the newspaper quoted a high-ranking NSA official as saying.

Der Spiegel reported that leaked NSA documents showed that Merkel’s phone had appeared on a list of spying targets since 2002, and was still under surveillance weeks before Obama visited Berlin in June.

Meanwhile, several thousand protesters gathered in Washington Saturday to push for new US legislation to curb the NSA’s activities.

Swiss President Ueli Maurer warned that the scandal risked “undermining confidence between states.” “We don’t know if we’re only seeing the tip of the iceberg or if other governments are acting in the same ruthless manner,” he told the Schweiz Sonntag weekly.