US President George W Bush has again defended his decision to allow eavesdropping on Americans in the wake of the 2001 terror attacks.
Speaking at a press conference, Mr Bush also repeated that he would continue to authorise the secret monitoring.
He also urged Congress to renew the Patriot Act, the top US anti-terror law, saying it provided officials with the tools to protect Americans.
"We cannot afford to be without this law for a single moment," he said.
It was not in the best interests of the country for people to "play politics" with the Patriot Act, he said, while answering reporters' questions.
The legislation has cleared the House of Representatives, but the Senate has rejected an attempt to reauthorize several sections of the bill. The legislation is due to expire at the end of the month.
'Helping the enemy'
Mr Bush also said he expected a "full investigation" into who leaked information about the wiretap programme.
"My personal opinion is it was a shameful act for someone to disclose this very important programme in a time of war," he said.
"The fact that we're discussing this programme is helping the enemy," he added.
The New York Times reported last Friday that Mr Bush had signed a secret presidential order following the 11 September 2001 attacks, allowing the National Security Agency to track the international telephone calls and e-mails of hundreds of people without referral to the courts.
Previously, surveillance on American soil was generally limited to foreign embassies.
Mr Bush emphasised that only international calls were monitored without a court order - those originating in the US, or those placed from overseas to individuals living in the US.
He reminded reporters that calls placed and received within the US could be monitored under orders granted by a secret court under the provisions of the Foreign Intelligence Surveillance Act.
The president, struggling with low approval ratings and public discontent with the US death toll in Iraq, also defended his decision to invade the country, saying "it wasn't a mistake" and that "history will judge".
On Sunday, in his fifth speech on Iraq in the past few weeks, Mr Bush appealed to Americans not to give in to despair over the war.