The head of the UN nuclear watchdog urged NATO nations Tuesday to end their dependence on nuclear weapons, as the military alliance launched a re-think of its future direction.

"You have to decrease heavily your reliance on nuclear weapons," the head of the International Atomic Energy Agency Mohamed El Baradei told NATO officials and experts in Brussels.

He said that by relying on a nuclear deterrant, NATO was sending the wrong message to the world that "we need to develop nuclear weapons".

"Insisting that nuclear is the supreme guarantee is the absolute wrong message to the rest of the world," said the Egyptian-born Nobel peace laureate, who is stepping down in November after 12 years in office.

NATO Secretary General Jaap de Hoop Scheffer rejected the call.

"It is crystal clear that NATO will continue to have a mix of nuclear and conventional means," he told reporters later. "As far as NATO is concerned, I don't think there will be a change.

"I would not be in favour of such a change," said Scheffer, who hands over the reins at NATO to former Danish premier Anders Fogh Rasmussen at the end of the month.

On Monday, Russian President Dmitry Medvedev and US President Barack Obama signed a declaration pledging to reach a new nuclear arms reduction pact to replace the 1991 START accord.

El Baradei's remarks came as NATO launched debate on a new "strategic concept".

NATO's current strategic concept -- which equips the alliance to face security challenges and guides its political and military development -- is a decade old, having been agreed in Washington in April 1999.

It mentions nuclear weapons as an essential deterrent.

The new text will have to take into account challenges like cyber attacks, climate change and energy security, as well as developments in terrorism since the September 11, 2001 attacks in the United States.

It could be unveiled at NATO's next summit due in Lisbon, Portugal late next year.