The deal, known as the United Kingdom-United States of America Agreement, calls for the United States, Britain, Canada, New Zealand and Australia to share intelligence and especially cooperate in intercepting electronic communications, including electronic signals not normally used in communication.
The five cooperating countries are known as the Five Eyes alliance.
The NSA is the U.S. government agency whose electronic surveillance and data mining is at the center of the scandal.
British newspaper The Guardian initially reported the existence of a program that collects data on all phone calls made on the Verizon network. Later in the week, The Guardian and The Washington Post reported the existence of a separate top-secret program, code-named PRISM, that collects the Internet data of foreigners from major Internet companies.
Edward Snowden -- a 29-year-old former CIA computer technician and government contractor working until recently at an NSA facility in Hawaii -- said Sunday he leaked the top-secret information because "the public needs to decide whether these programs and policies are right or wrong."
The U.S. Justice Department has begun the process of charging him with disclosing classified information.
Canada and New Zealand wouldn't say if they used data gathered through PRISM. Australia had no immediate comment.
British Foreign Secretary William Hague, who canceled a trip to Washington to address Parliament on the issue, spoke about a report in The Guardian Monday that Britain's Government Communications Headquarters intelligence agency used the PRISM espionage program to circumvent British law and snoop on emails and phone calls since at least June 2010.
"It has been suggested GCHQ uses our partnership with the United States to get around U.K. law, obtaining information that they cannot legally obtain in the U.K. I wish to be absolutely clear that this accusation is baseless," Hague said Monday.
"Any data obtained by us from the U.S. involving U.K. nationals is subject to proper U.K. statutory controls and safeguards," he said.
But he admitted personally approving "hundreds" of intelligence missions "every year" -- many involving U.S. spies.
Canadian Defense Minister Peter MacKay declined to say if Canada was using PRISM data but said Canada's own top-secret online and phone metadata surveillance program, known as the Communication Security Establishment, was "prohibited" from looking at Canadians' information.
"This program is very much directed at activities outside the country, foreign threats in fact," CTV News quoted him as telling the House of Commons.
MacKay said Canada's CSE program has operated "for years."
New Zealand Prime Minister John Key refused to rule out if his country could have been involved in the PRISM spy program.
"We don't comment on security matters," Television New Zealand quoted him as saying.
Australian government officials had no immediate comment.