ATHENS (AFP) - Greece on Monday said it was baffled by reports of covert US surveillance of European Union diplomatic missions and added that it would request "clarification" if there was any truth behind them.

"(Greece) is unable to grasp information that has come to light regarding surveillance of, among others, Greek diplomatic missions from the services of a friend and ally," foreign ministry spokesman Constantinos Koutras said in statement.

"The relevant Greek services have already begun to examine these reports and the necessary clarifications will be requested depending on the outcome," spokesman Koutras said.

German news weekly Der Spiegel has reported that the US National Security Agency (NSA) carried out covert surveillance on EU diplomatic missions, basing its report on confidential documents, some of which it had been able to consult via fugitive US leaker Edward Snowden.

The European Union, Paris and Berlin have angrily demanded answers over the allegations.