Image caption Details of the surveillance programmes were leaked by former NSA contractor Edward Snowden

The US government searched for detailed information on fewer than 300 phone numbers last year, according to a government paper.

They were among millions of phone and email records collected by the National Security Agency (NSA) in 2012, it says.

The paper adds that such searches led to two men who were plotting to attack New York's subway system in 2009.

The newly declassified paper has been circulated within the government by US intelligence agencies.

It was made public by the Senate Intelligence Committee on Sunday.

The document appears to be an attempt to counter accusations that the government went too far in investigating potential militant plots.

The administration insists that even though the NSA collects massive amounts of data on message traffic from US-based telephone and internet companies, such data collection is legal, subject to tight controls and does not intrude on the privacy of ordinary Americans - and that gathered data is destroyed every five years.

The paper repeats assertions by administration spokesmen that NSA email and telephone data-collection programmes helped disrupt "dozens of potential terrorist plots here in the homeland and in more than 20 countries around the world".

No details about the plots or the countries involved are revealed.

The paper's release follows a testing week for US intelligence officials who testified in Congress, defending programmes that were unknown to the public - and some lawmakers - until they were revealed by a series of stories in the Guardian and the Washington Post newspapers.

These were based on information leaked by former NSA contractor Edward Snowden, who is in hiding in Hong Kong.