Barack Obama has defended top secret National Security Agency spying programmes as legal and transparent - even though they are authorised in secret.
"It is transparent," the US President said in an interview. "That's why we set up the FISA court," he added, referring to the secret court set up by the Foreign Intelligence Surveillance Act that authorises two recently leaked programmes - one that gathers US phone records and another designed to track the use of US-based internet servers by foreigners with possible links to terrorism.
The location of FISA courts is secret, the sessions are closed, and the orders that result from hearings in which only government lawyers are present are classified.
"We're going to have to find ways where the public has an assurance that there are checks and balances in place ... that their phone calls aren't being listened into, their text messages aren't being monitored, their emails are not being read by some big brother somewhere," Mr Obama said.
He was in Northern Ireland for a meeting of leaders of allied countries. As he arrived, the latest series of Guardian articles drawing on the leaks claimed that British eavesdropping agency GCHQ repeatedly hacked into foreign diplomats' phones and emails with US help, in an effort to get an edge in high-stakes negotiations.
Mr Obama's announcement followed an online chat on Monday by Edward Snowden, the former NSA systems analyst contractor who leaked documents revealing the scope of the two programmes to the Guardian and the Washington Post. He accused members of Congress and administration officials of exaggerating their claims about the success of the data gathering programmes, including pointing to the arrest of would-be New York subway bomber Najibullah Zazi in 2009.
Mr Snowden said Zazi could have been caught with narrower, targeted surveillance programmes - a point Mr Obama conceded in his interview without mentioning Mr Snowden.
"We might have caught him some other way," Mr Obama said. "We might have disrupted it because a New York cop saw he was suspicious. Maybe he turned out to be incompetent and the bomb didn't go off. But at the margins we are increasing our chances of preventing a catastrophe like that through these programmes."
Mr Obama also said he wanted to encourage a national debate on the balance between privacy and national security - a topic renewed by Mr Snowden's disclosures.
The President repeated earlier assertions that the programmes were a legitimate counter-terror tool and that they were completely non-invasive to people with no terror ties. He also said he has created a privacy and civil liberties oversight board. "I'll be meeting with them. And what I want to do is to set up and structure a national conversation, not only about these two programmes, but also the general problem of data, big data sets, because this is not going to be restricted to government entities," he said.