French President Francois Hollande has said allegations that the U.S. bugged European embassies could threaten a huge planned trade deal, BBC News reported.

Negotiations over the EU-US pact, the biggest bilateral deal ever negotiated, are due to start on July 8.

Hollande said there could be no negotiations without guarantees spying would stop "immediately".

U.S. Secretary of State John Kerry said earlier that activities to protect national security were "not unusual".

German Chancellor Angela Merkel's spokesman, Steffen Seibert, said "bugging friends is unacceptable... we are no longer in the Cold War". He added that Germany wanted the deal to go ahead but "mutual trust is necessary in order to come to an agreement".

The allegations of U.S. security services bugging EU missions and the embassies of friendly European countries - including the French, Italian and Greek embassies - come from documents apparently leaked by an ex-CIA analyst.

Edward Snowden has been charged in the US with theft of government property, unauthorized communication of national defense information and willful communication of classified communications intelligence.

He is believed to be at an airport in Moscow, and is seeking a destination safe from prosecution by the U.S. authorities.

Green parties in France and Germany have called on their governments to offer Mr Snowden asylum.