Speaking at the launch of a campaign aimed at increasing awareness of the dangers of weapons of mass destruction on Thursday in London, Gorbachev also said the US invasion of the oil-rich country was undermining democracy.
Credited with helping bring the Cold War and the nuclear arms race to an end, the former Soviet leader appealed to all countries holding stocks of nuclear weapons to destroy them to avoid the risk that they may fall into the wrong hands.
"Should the extremists gain access to weapons of mass destruction, the threat would become catastrophic," he said.
In an interview with Britain's Channel Four television, Gorbachev also criticised Russian President Vladimir Putin's plan to abolish voting for regional governors.
He expressed fears that the measure mooted by Putin in the wake of the Beslan school siege that killed more than 300 people, could end up stripping the Russian people of democratic rights.
"I have spoken of my concerns," Gorbachev said. "We are wiping out an important - perhaps, the most important - right of the people: The right to choose."
"I believe there should be a big debate about this. It needs to be talked through. The president is concerned, and all of society is concerned, that sometimes elections did result in the election of people who had no business in governorship.
"But the solution is not to abolish elections. You should give the president the power to intervene if the governor has lost the moral right to power," he said.
Putin's plan for scrapping elections for regional governors has been roundly criticised by liberal opponents, who accuse the president of exploiting the hostage crisis to consolidate his own power.