The U.S. Senate has blocked a bill that would have ended the bulk collection of Americans' phone records by the National Security Agency (NSA). It also failed to authorize a temporary extension of the current legislation, BBC News reports.

Senators are to meet again on May 31 - a day before the bill is due to expire.

A U.S. appeals court has already ruled the bulk collection illegal.

The NSA's spying was leaked by Edward Snowden, a former NSA contractor who has since fled to Russia.

The NSA has collected data about numbers called and times, but not the content of conversations. It also allegedly spied on European firms.

Among individuals targeted was German Chancellor Angela Merkel.

The White House has pressed the Senate to back the a bill passed by the House of Representatives - the Freedom Act - which would end bulk collection of domestic phone records. These records would remain with telephone companies subject to a case-by-case review.

The 57-42 Senate vote fell short of the 60-vote threshold.

Another vote held over a two-month extension to the existing programs - Section 215 of the USA Patriot Act - also failed to reach the threshold.

Supporters of the proposed Freedom Act, including privacy and civil rights advocates, say it protects privacy while preserving national security powers.

The Patriot Act was passed after the 9/11 attacks and which will expire on June 1.

The Snowden revelations in June 2013 caused an international outcry, despite U.S. administrations insisting the program has been fully authorized.

The measures have been repeatedly approved in secret by a national security court since 2006.