US President Barack Obama has vowed to pursue further nuclear arms cuts with Russia, as world leaders gather for a nuclear security summit in South Korea.
Mr Obama urged China to follow suit and issued stern warnings to North Korea and Iran in their nuclear standoffs with the West.
He acknowledged the US currently has more warheads than necessary.
Mr Obama held out the prospect of new reductions in the US arsenal as he sought to rally world leaders for additional concrete steps against the threat of nuclear terrorism.
"We can already say with confidence that we have more nuclear weapons than we need," Mr Obama told students at South Korea's Hankuk University before the summit opened in Seoul.
Mr Obama met Russia's outgoing leader, Dmitry Medvedev, on the sidelines of the summit, with missile defence in Europe, Iran and the conflict in Syria topping their agenda.
He pledged a new arms-control push with incoming Russian President Vladimir Putin when they meet in May.
But any further reductions would face stiff election-year opposition from Republicans in Congress, who already accuse him of weakening the US’s nuclear deterrent.
Mr Obama laid out his latest strategy against the backdrop of nuclear defiance from North Korea and Iran, twin challenges that have clouded his overall nuclear agenda and the summit in Seoul.
He set expectations high in a 2009 speech in Prague when he declared it was time to seek "a world without nuclear weapons", but acknowledged at the time it was a long-term goal.
In Seoul, Mr Obama made clear that he was committed to that notion, saying "those who deride our vision, who say that ours is an impossible goal that will be forever out of reach", were wrong.
Though Mr Obama was vague on exactly how such a vision would be achieved, he voiced confidence the US and Russia, which reached a landmark arms-control treaty in 2010, "can continue to make progress and reduce our nuclear stockpiles".
"I firmly believe that we can ensure the security of the United States and our allies, maintain a strong deterrent against any threat, and still pursue further reductions in our nuclear arsenal," he said.
But another arms accord with Moscow will be a tough sell to US conservatives who say Mr Obama has not moved fast enough to modernise the US strategic arsenal, a pledge he made in return for Republican votes that helped ratify the START treaty.
The US and Russia are the two biggest nuclear powers, possessing thousands of warheads between them.
Chinese President Hu Jintao indicated to Mr Obama during a one-on-one meeting that he took the North Korean nuclear stand-off very seriously and was registering his concern with Pyongyang.
Mr Obama said North Korea could be hit with tighter sanctions if it goes ahead with the rocket launch, but there are doubts that China will back another UN Security Council resolution against North Korea.
North Korea says the rocket will send a satellite into space, but South Korea and the US say it is a ballistic missile test.
Ahmadinejad tells US to change policy
Meanwhile, Iranian President Mahmoud Ahmadinejad said today the US could no longer dictate policy to the rest of the world and relations between NATO and Pakistan would become more unstable.
"NATO and the United States should change their policy because the time when they dictate their conditions to the world has passed," Mr Ahmadinejad said in a speech during a conference on Afghanistan's economy in the capital of neighbouring Tajikistan.
"Relations between NATO and Pakistan, their unsteadiness and instability, will only grow," he said.
