A presidential advisory panel says telephone information collected in bulk by the National Security Agency and used in terror investigations "was not essential to preventing attacks" and has proposed sweeping changes to US government surveillance programmes.

Under the proposals, court orders would be also required before the information could be searched.

In a 300-page report, the five-member panel also proposed greater scrutiny of decisions to spy on friendly foreign leaders, a practice that has outraged US allies around the world.

While the panel's 46 recommendations broadly called for more oversight of the government's vast spying network, few programmes would be ended. There is also no guarantee that the most stringent recommendations will be adopted by President Barack Obama, who authorised the panel but is not obliged to act on its findings.

The task force said it sought to balance America's security with the public's privacy rights.