LONDON, October 25 (Itar-Tass) - The U.S. National Security Agency (NSA) monitored phone calls of 35 world leaders, according to a classified document provided by whistleblower Edward Snowden, The Guardian website reports on Friday.

The confidential memo reveals that the NSA encourages senior officials in its “customer” departments, such the White House, State and the Pentagon, to share their “Rolodexes” so the agency can add the phone numbers of leading foreign politicians to their surveillance systems.

“In one recent case,” the memo notes, “a US official provided NSA with 200 phone numbers to 35 world leaders … Despite the fact that the majority is probably available via open source, the PCs [intelligence production centres] have noted 43 previously unknown phone numbers. These numbers plus several others have been tasked.” The document, dated October 2006, acknowledges that eavesdropping on the numbers had produced “little reportable intelligence.”

Previous reports about the possible tapping of German Chancellor Angela Merkel’s mobile phone came as a bombshell. Merkel on Wednesday called U.S. President Barack Obama and demanded explanations from him. The White House pledged that “The United States is not monitoring and will not monitor the communications of Chancellor Merkel.” However, Berlin officials emphasised that this wording did not rule out that this had already happened in the past. The European press reports previously said that U.S. wiretapping had also been conducted in France and Italy.