The White House has acknowledged the need for additional "constraints" on US intelligence gathering, amid reports the nation had spied on its allies.

President Barack Obama's spokesman Jay Carney said a review of the US intelligence programmes would be done by the end of the year.

"The issues that are part of the review look at how we can better balance our security needs and the security needs of our allies against the real privacy concerns that we all share," Mr Carney said.