Former vice-president – not persuaded by argument that program was legal – urges Congress and Obama to amend the laws

The National Security Agency's blanket collection of US citizens' phone records was "not really the American way", Al Gore said on Friday, declaring that he believed the practice to be unlawful.

In his most expansive comments to date on the NSA revelations, the former vice-president was unsparing in his criticism of the surveillance apparatus, telling the Guardian security considerations should never overwhelm the basic rights of American citizens.

He also urged Barack Obama and Congress to review and amend the laws under which the NSA operated.

"I quite understand the viewpoint that many have expressed that they are fine with it and they just want to be safe but that is not really the American way," Gore said in a telephone interview. "Benjamin Franklin famously wrote that those who would give up essential liberty to try to gain some temporary safety deserve neither liberty nor safety."

Since the 2000 elections, when Gore won the popular vote but lost the presidency to George W Bush, the former vice-president has tacked to the left of the Democratic party, especially on his signature issue of climate change.

Gore spoke on Friday from Istanbul where he was about to lead one of his climate change training workshops for 600 global activists. Such three-day training sessions on behalf of the Climate Reality Project are now one of his main concerns.

Unlike other leading Democrats and his former allies, Gore said he was not persuaded by the argument that the NSA surveillance had operated within the boundaries of the law.

"This in my view violates the constitution. The fourth amendment and the first amendment – and the fourth amendment language is crystal clear," he said. "It is not acceptable to have a secret interpretation of a law that goes far beyond any reasonable reading of either the law or the constitution and then classify as top secret what the actual law is."

Gore added: "This is not right."

The former vice-president was also unmoved by some recent opinion polls suggesting public opinion was in favour of surveillance

"I am not sure how to interpret polls on this, because we don't do dial groups on the bill of rights," he said.

He went on to call on Barack Obama and Congress to review the laws under which the NSA expanded its surveillance. "I think that the Congress and the administration need to make some changes in the law and in their behaviour so as to honour and obey the constitution of the United States," he said. "It is that simple."

He rejected outright calls by the Republican chair of the house homeland security committee, Peter King, for prosecution of journalists who cover security leaks, such as the Guardian's Glenn Greenwald.

Gore did say, however, that he had serious concerns about some aspects of the testimony offered by national intelligence director James Clapper during testimony to the Senate intelligence committee last March.

Clapper, in response to pointed questions from Democratic senator Ron Wyden, had said during that appearance that the NSA did not collect data on Americans.

"I was troubled by his direct response to Senator Wyden's very pointed question," Gore said. "I was troubled by that."

Gore has long had qualms about the expansion of the surveillance state in the digital age. He made those concerns public this year in his latest book, The Future: Six Drivers of Social Change, in which he warned: "Surveillance technologies now available – including the monitoring of virtually all digital information – have advanced to the point where much of the essential apparatus of a police state is already in place."

Within hours of the Guardian's first story about the NSA, the former vice-president tweeted: "In digital era, privacy must be a priority. Is it just me, or is secret blanket surveillance obscenely outrageous?

He said on Friday: "Some of us thought that it was probably going on, but what we have learned since then makes it a cause for deep concern."