European leaders united in anger as they attended a summit overshadowed by reports of widespread US spying on its allies, allegations German Chancellor Angela Merkel said had shattered trust in the Obama administration and undermined the crucial trans-Atlantic relationship.

France, which also vocally objected to allies spying on each other, asked that the issue of reinforcing Europeans' privacy in the digital age be added to the agenda of the two-day summit.

After summit talks on Thursday that lasted until after midnight, Herman Van Rompuy, European Council president, announced at a news conference that France and Germany were seeking bilateral talks with the US to resolve the dispute over "secret services" electronic spying by the end of this year.

"What is at stake is preserving our relations with the United States," French President Francois Hollande told reporters at his own early-morning news conference. "They should not be changed because of what has happened. But trust has to be restored and reinforced."

"It's become clear that for the future, something must change, and significantly," Merkel said. "We will put all efforts into forging a joint understanding by the end of the year for the cooperation of the [intelligence] agencies between Germany and the US, and France and the US, to create a framework for the cooperation."

Guardian spy reports

The British newspaper The Guardian said on Thursday it obtained a confidential memo suggesting the NSA was able to monitor 35 world leaders' communications in 2006.

The memo said the NSA encouraged senior officials at the White House, Pentagon and other agencies to share their contacts so the spy agency could add foreign leaders' phone numbers to its surveillance systems, the report said.

The Guardian did not identify who reportedly was eavesdropped on.

Other European leaders arriving for the 28-nation meeting echoed Merkel's displeasure.

Swedish Prime Minister Fredrik Reinfeldt called it "completely unacceptable" for a country to eavesdrop on an allied leader, and Dutch Prime Minister Mark Rutte called the spy allegations "exceptionally serious".

"We want the truth," Italian Prime Minister Enrico Letta told reporters. "It is not in the least bit conceivable that activity of this type could be acceptable."

Echoing Merkel, Austria's foreign minister, Michael Spindelegger, said, "We need to re-establish with the US a relationship of trust, which has certainly suffered from this."

Source: Al Jazeera and agencies