Barack Obama, the US president and Chinese President Hu Jintao are holding talks expected to focus on US frustrations with China's slow progress in pushing North Korea to comply with international obligations.
In brief remarks ahead of the bilateral meeting on the sidelines of the Nuclear Security Summit in the South Korean capital Seoul on Monday, Obama said he was looking forward to a frank and constructive meeting.
"Obviously of great importance to us, and I hope to you as well, is the situation in North Korea, and the situation in Iran," Obama said.
"We both had an interest in making sure that international norms surrounding non-proliferation and preventing destabilising nuclear weapons is very important."
"We can already say with confidence that we have more nuclear weapons than we need. "
- US President Barack Obama
While the official agenda of the summit is to strengthen measures to track the movement of nuclear materials worldwide, much of the dialogue is expected to focus on efforts to get North Korea to back off a planned rocket launch and return to disarmament talks.
"I think, co-operation and co-ordination between the United States and China is very important not only to the interest of our two countries but to the interest of the world," he added.
North Korea announced earlier this month that it would send a satellite into space aboard a long-range rocket.
Pyongyang has said the launch is part of its peaceful space programme and says a new southern flight path is meant to avoid other countries; previous rockets have been fired over Japan.
Obama has urged North Korean leaders to abandon their rocket plan or risk jeopardising their country's future and thwarting a recent US pledge of food aid in return for nuclear and missile test moratoria, considered a breakthrough after years of deadlock.
The Seoul Nuclear Security Summit, attended by nearly 60 world leaders, will start with a working dinner on Monday night and continues until Tuesday.
Al Jazeera's Harry Fawcett, reporting from Seoul, said: "This was a speech by President Obama to unify the big themes of his visit; he used the speech to help achieve his dream of a nuclear free world."
Earlier in the summit, Obama said that he was pushing for "a world without nuclear weapons" and was committed to deterring nuclear proliferation, while on a visit to Seoul for the two-day 53-nation nuclear summit.
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," Obama told students at South Korea's Hankuk University a few hours before a global nuclear security summit opened in Seoul.
Obama caught telling Medvedev that he will have "more flexibility" with missile defence after US elections
Obama told students that he was confident the United States and Russia could jointly reduce their stockpiles of nuclear weapons, building on the successful extension of arms control agreements known as START.
The White House said nuclear weapons reduction continued to be a priority in US relations with Russia, and that Obama would raise it with president-elect Vladimir Putin when they meet in May.
But the US president sent an early message along when he told Russia's President Dmitry Medvedev that he would have more flexibility after the November presidential election to deal with the contentious issue of missile defense, a candid assessment of political reality that was picked up by a microphone without either leader apparently knowing.
"This is my last election," said Obama. "After my election, I have more flexibility.''
Medvedev replied that he's pass the information along to Putin.
But Obama seemed anxious to deal with Iran on a more immediate timeline.
"There is time to solve this diplomatically. It is always my preference to solve these issues diplomatically," he said.
"Iran's leaders must understand that there is no escaping the choice before it. Iran must act with the seriousness and sense of urgency that this moment demands," Obama said. "Iran must meet its obligations."
Iran insists there is no military element to its programme, but Western powers fear it is constructing nuclear weapons.
Neither Iran nor North Korea is participating in the summit.
The summit agenda is to be expanded to include a wide variety of radiological materials which terrorists could use to make a dirty bomb, one that spreads radiological contamination rather than initiating a nuclear explosion.
Source: Al Jazeera and agencies