European politicians visiting Washington to investigate claims of mass surveillance by America in Europe say United States explanations that all allies spy on each other are not enough.
The most senior intelligence advisers to the German chancellor are also in Washington to meet their counterparts at the White House following reports the Americans had been monitoring Angela Merkel's mobile phone.
The fact Ms Merkel has sent two of the most important people in her immediate circle to the meeting is seen as an indication of how seriously she is taking the matter, the BBC reports.
A spokesperson for the European delegation, British European Parliament member Claude Moraes, says it is not acceptable to dismiss spying on friendly nations as normal.
"Spying has always existed but we have said repeatedly that friend on friend spying is not something that is easily tolerable if it doesn't have a clear purpose, and it if happens there needs to be some kind of justification, he says.
This week's meetings are about how to rebuild trust, while separate meetings next week between the heads of the actual spy agencies are expected to be more about the detail of how the two countries' agencies might or might not work in harmony.
Meanwhile, new allegations have emerged that the US National Security Agency is secretly tapping the communication links between Yahoo and Google, giving it access to hundreds of millions of user accounts worldwide.
Documents published in the Washington Post newspaper show millions of records were gleaned daily from the internet giants' internal networks, the BBC reports.
The United States is facing growing anger from its international allies because of its spying activities.
Allegations of Russian spying
Meanwhile, as the United States and Europe continue to argue over spying allegations, it's now been claimed that Russia also tried to spy on world leaders.
Italian media are reporting that the Russian secret service tried to access the communications and computer records of G20 leaders in St Petersburg last month.
A spokesperson for Russian president Vladimir Putin has denied the allegations.
