German spy chiefs will travel to the United States next week to demand answers following allegations that US intelligence has been tapping Chancellor Angela Merkel’s mobile phone.

German spy chiefs will travel to the United States next week to demand answers following allegations that US intelligence has been tapping Chancellor Angela Merkel's mobile phone.

Documents leaked by former US intelligence contractor Edward Snowden showing sweeping US surveillance on ordinary citizens' Internet searches and telephone records have already sparked outrage worldwide.

But the tension has been intensified after allegations that world leaders including the presidents of Brazil and Mexico have been among spying targets.

This week, the scandal widened to Europe, with allegations that Merkel's phone was being tapped, prompting Berlin to summon the US ambassador -- a highly unusual move between the close allies.

"High-ranking government representatives will go rapidly to the United States in order to push forward discussions with the White House and the NSA (National Security Agency) on the allegations raised recently," Georg Streiter, the chancellor's deputy spokesman, said Friday.

German media quoting sources close to the intelligence service reported Saturday that the delegation will include top officials from the German secret service.

Germany and Brazil are also working on a UN General Assembly resolution to highlight international anger at US data snooping in other countries, diplomats said Friday.