Media playback is unsupported on your device Media caption A summary of US spying allegations brought about by Edward Snowden's leak of classified documents

A German delegation of officials is in Washington for talks following claims that the US National Security Agency monitored Chancellor Angela Merkel's mobile phone.

The chancellor's foreign policy adviser and Germany's intelligence co-ordinator will hold talks at the White House.

The head of US intelligence has defended the monitoring of foreign leaders as a key goal of operations.

The US is facing growing anger over reports it spied on its allies abroad.

It has also been reported that the NSA monitored French diplomats in Washington and at the UN, and that it conducted surveillance on millions of French and Spanish telephone calls, among other operations against US allies.

Spanish Prime Minister Mariano Rajoy said that if Spain had been a target of the NSA, this would be "inappropriate and unacceptable between partners".

Analysis The measure of how seriously Chancellor Merkel takes the matter is that she has sent two of the most important people in her immediate circle of advisers: her foreign policy adviser, Christoph Heusgen, and the German government's intelligence co-ordinator, Guenter Heiss. Next week, the heads of the actual spying agencies go to meet their opposite numbers in Washington. This week's meetings are more about how to rebuild trust, while next week's agenda will be more about the detail of how the two countries' agencies might or might not work more in harmony. The US has an agreement to share intelligence with Britain, New Zealand, Australia and Canada. It is not clear if Germany wants to be part of that. There have been commentators in America saying that Germany is in a different position from the other countries mentioned because its future relationship with China is not clear. On this argument, Germany's close trade links with China might make it loath to support the US in any future trans-Pacific confrontation. Media detects mixed messages

However, NSA director Gen Keith Alexander said "the assertions... that NSA collected tens of millions of phone calls are completely false".

The revelations stem from documents leaked by fugitive ex-US intelligence contractor Edward Snowden, who now lives in Russia and is wanted in the US in connection with the unauthorised disclosures.

On Wednesday, fresh leaks from Mr Snowden showed that the NSA had hacked into links between data centres belonging to Yahoo and Google, the Washington Post reports.

Millions of records were gleaned daily from the internet giants' internal networks, according to the documents given to the Post by Mr Snowden.

The data, which ranged from "metadata' to text, audio and video, were then sifted by an NSA programme called Muscular, operated with the NSA's British counterpart, GCHQ, the documents say.

However, the director of the NSA said in a TV interview to be broadcast on Wednesday that the agency had not had access to either company's servers.

"We are not authorised to go into a US company's servers and take data," Keith Alexander told Bloomberg TV.

"They [Yahoo and Google] are compelled to work with us," Gen Alexander added.

Also on Wednesday, the UN said it had received assurances that its communications "are not and will not be monitored" by American intelligence agencies.

'Basic tenet'

German media have reported that the US bugged German Chancellor Merkel's phone for more than a decade - and that the surveillance only ended a few months ago.

Germany's delegation includes Christoph Heusgen, Mrs Merkel's foreign policy adviser, and Guenter Heiss, the secret service co-ordinator, said Caitlin Hayden, a spokeswoman for the US National Security Council.

US National Security Adviser Susan Rice, Director of National Intelligence James Clapper and Lisa Monaco, assistant to the president for homeland security and counterterrorism, are also expected to take part.

Ms Hayden said the meeting was part of the agreement reached between President Barack Obama and Chancellor Merkel last week to deepen US-German co-operation on intelligence matters.

Mr Clapper and Gen Alexander testified before the intelligence panel of the House of Representatives on Tuesday.

How intelligence is gathered Accessing internet company data

Tapping fibre optic cables

Eavesdropping on phones

Targeted spying Read more in our in-depth report

Gen Alexander said much of the data cited by non-US news outlets was actually collected by European intelligence services and later shared with the NSA.

Meanwhile, Mr Clapper told lawmakers that discerning foreign leaders' intentions was "a basic tenet of what we collect and analyse".

He said that foreign allies spy on US officials and intelligence agencies as a matter of routine.

Mr Clapper said the torrent of disclosures about American surveillance had been extremely damaging and that he anticipated more.

But he said there was no other country that had the magnitude of oversight that the US had, and that any mistakes that had been made were human or technical.

The BBC's Jonny Dymond in Washington says if anyone was expecting apologies or embarrassment from the leaders of America's intelligence community, they were in for a disappointment.

Media playback is unsupported on your device Media caption James Clapper said knowing what foreign leaders were thinking was critical to US policymaking

The intelligence pair were not given a tough time by the committee but that sentiment is turning within Congress toward tightening up the reach of American intelligence agencies, our correspondent says.

Meanwhile, the spokesman for Russian President Vladimir Putin has denied that Moscow used free USB memory sticks and mobile phone charging cables to spy on delegates attending the G20 Summit in St Petersburg last September.

Reports in two Italian newspapers suggested that the USB sticks and cables had bugs on them that could steal data from the delegates.

Spokesman Dmitri Peskov said the reports were an attempt to distract from the problems between European countries and the US.