EU leaders gather for a summit in Brussels on Friday.

They were due to discuss the migration dilemma but instead the talks have been overshadowed by a row over spying.It follows claims that the phone of German Chancellor Angela Merkel and millions of French calls have been monitored by the US National Security Agency.She warned the US that eavesdropping on allies was unacceptable, saying "spying on friends, that's just not done".

Merkel has demanded a complete explanation of the phone tapping claims which emerged in the German media.Paris and Berlin are united in their outrage.Merkel and French President Francois Hollande want to hold talks with the US by the end of the year.

White House spokesman Jay Carney said there was no doubt the revelations had caused tensions between the US and its allies.He reiterated that Obama had assured the German Chancellor that her phone is not being listened to now and will not be in the future but that statement still left open the question of whether calls had been listened to in the past.