President Barack Obama used a speech in Berlin yesterday to call on Russia to revive the push for a world without nuclear arms by agreeing to target further reductions of up to one third of deployed nuclear weapons.

Speaking in Berlin where John F Kennedy and Ronald Reagan gave rousing Cold War speeches, Mr Obama urged Russia to help build on the New START treaty that requires both countries to cut stockpiles of deployed nuclear weapons to 1550 each by 2018.

"After a comprehensive review I have determined that we can ensure the security of America and our allies, and maintain a strong and credible strategic deterrent, while reducing our deployed strategic nuclear weapons by up to one third," he said.

"I intend to seek negotiated cuts with Russia to move beyond Cold War nuclear postures," Mr Obama said at the Brandenburg Gate, which once stood alongside the Berlin Wall that divided the communist east and the capitalist west.

Mr Obama's vision of a "world without nuclear weapons" set out in a speech in Prague in 2009, three months into his presidency, earned him the Nobel Peace Prize. But his mixed results so far have fuelled criticism that the prize may have been premature.

Experts said reducing the nuclear arsenal makes strategic and economic sense. But Mark Fitzpatrick at the International Institute for Strategic Studies said Mr Obama faces major obstacles "including a recalcitrant Russia and a reluctant Senate".

President Vladimir Putin, speaking in St Petersburg, made no direct comment but voiced worry about US missile defences and high-precision weapons.

Moscow sees nuclear deterrents as the safeguard of national security. It is worried about the West's superior conventional weapons and Nato plans for a missile defence system in Europe.

"High-precision conventional weapons systems are being actively developed ... States possessing such weapons strongly increase their offensive potential," said Mr Putin.