The head of the UN's nuclear watchdog warned on Monday there was a real threat that terrorist groups could resort to nuclear weapons.
"We worry about sub-national groups, extremist groups acquiring nuclear weapons. It is a nightmare because they will use it," said Mohamed ElBaradei, the head of the International Atomic Energy Agency (IAEA).
ElBaradei was speaking at a conference on nuclear disarmament in Berlin organised by the Social Democrats, who are partners in Germany's ruling coalition.
He said that in the aftermath of the September 11 attacks on the United States, extremists had become more sophisticated and were trying to lay their hands on nuclear arms.
"We have seen the interest of these groups in acquiring nuclear weapons."
ElBaradei said the nuclear arms race was still being fuelled by the fact that many nations saw such weapons as a status symbol.
"There is still an aura of power, a status of prestige that comes with nuclear weapons," he said.
German Foreign Minister Frank-Walter Steinmeier warned that the more governments developed nuclear arms, the greater the risk would be that terrorist groups could gain access to them.
But, he said, the primary problem would be an escalation of the international nuclear arms race over the next decade, particularly if "the Iranian and North Korean nuclear crises were not resolved.