European politicians have said they want a new deal with Washington to defuse a damaging spy row.

The aim should be to agree rules for intelligence gathering rather than seek a pointless confrontation, Belgian Prime Minister Elio di Rupo said, backtracking from earlier outrage expressed by Europe's US allies.

"The objective must remain the same - to fight against terrorism but also respect privacy," Mr di Rupo said as he arrived for the second day of an EU leaders summit which has been dominated by revelations of US spying operations across Europe.

The revelations, topped by reports that German Chancellor Angela Merkel's mobile phone had been tapped, have sparked outrage in Europe.

"Spying between friends, that's just not done," Ms Merkel said.

"We need trust between partners and such trust needs to be re-established."

US homeland security advisor Lisa Monaco acknowledged that surveillance disclosures "have created significant challenges in our relationships with some of our closest foreign partners."

Ms Monaco added that "the president has directed us to review our surveillance capabilities."

Meanwhile, the Washington Post reported that the US has warned some foreign intelligence services that documents obtained by whistleblower Edward Snowden contain details of how they co-operate secretly with Washington.

Citing unnamed US officials, it said that some of the tens of thousands of documents harvested by the former NSA contractor contained sensitive material about programmes against countries such as Iran, Russia and China.