A statement agreed by the leaders says that "a lack of trust could prejudice" intelligence-gathering co-operation.

France and Germany are pushing for talks with the US to find a new "understanding" by the year's end.

German and French accusations that the United States has run spying operations in their countries dominated the meeting of EU leaders, with members calling for a full explanation and a review of the bloc's privacy laws.

The two-day Brussels summit, called to tackle a range of social and economic issues, will now be overshadowed by debate on how to respond to the alleged espionage by Washington against two of its closest European union allies.

For Germany the matter is particularly sensitive.

Government spokesman Georg Streiter said senior German officials will travel to the u.s. Shortly to talk with the white house and the national security agency about spying allegations, including how chancellor Angela Merkel's Cellphone was allegedly monitored by the NSA.

Germany's frustration follows outrage in France since le monde newspaper reported the NSA had collected tens of thousands of French phone records between December 2012 and January 2013.

French President Francois Hollande has made clear that he plans to put the spying issue on the summit agenda, although it is not clear what that will ultimately achieve.

While Berlin and Paris are likely to find sympathy among many of the EU's 28 member states, domestic security issues are not a competence of the European Union.