US intelligence chiefs have defended listening-in to the phone calls of world leaders.

They've appeared at a Congressional hearing, amid reports they monitored German Chancellor Angela Merkel's phone for over ten years - and may have spied on millions of phone calls in Spain and France.

National Intelligence Director James Clapper says all intelligence operations are essential to homeland security. At the hearing, Mr Clapper explained why monitoring goes on "For one, to determine, from an intelligence perspective, if what they're saying really gels with what's going on. It's invaluable for us to know where countries are coming from, what's going on, how that would impact us across a whole range of issues."

And he says that includes trying to understand the intentions of foreign leaders.

But Mr Clapper said the media had gotten it wrong on reports they had read about millions of calls listened to in France and Spain which, he said, actually related to information the US had been given through its collaboration with European agencies. He alleged reporters had misinterpreted the data they were leaked.

Adam Entous, the Wall Street Journal's National Security Correspondent explained the latest developments to Newstalk's Breakfast earlier:

They admitted that mistakes have been made - but said that all operations are essential to homeland security.

And NSA Director General Keith Alexander says reports that the agency spied on millions of phone calls across Europe are false: