North Korea vowed Tuesday to go ahead with a rocket launch, snubbing demands from US President Barack Obama and other world leaders who are in Seoul for a summit on combating nuclear terrorism.

The North's plan to launch a long-range rocket next month has overshadowed the 53-nation summit, which is meant to focus on the threat of uranium and other nuclear material from falling into the hands of terrorists.

Obama has devoted much of his three-day South Korean visit to its wayward neighbour, repeatedly denouncing the rocket launch while emphasising the United States is not hostile to the North's people.

North Korea responded Tuesday by saying it would go ahead with what it calls a peaceful satellite launch, saying every nation has this right, and called on Obama to drop his "confrontational mindset".

"The US head of state said he had no hostile intention towards us," said a Pyongyang foreign ministry spokesman quoted by the official KCNA news agency.

"But if that remark is genuine, he should abandon the confrontational mindset that tries to block us, and should have the courage to admit that we have as much right to launch our satellite as other countries do."

The North said it would judge whether Obama's remarks were genuine "or just another hypocrisy" depending on whether his country applies a double standard to the launch.

The United States, Japan, South Korea and other countries say the launch would in fact be a long-range missile test, banned under UN resolutions and breaching US-North Korean deal last month.

Obama on Monday made an unusual, direct appeal to the North's new leaders to "have the courage to pursue peace". There would be no more rewards for provocations, he said in reference to its launch.

Chinese President Hu Jintao, whose country is North Korea's sole major ally, also reportedly expressed serious concern at Pyongyang's plan during a meeting Monday with Obama.

On Tuesday's second and final day of the summit, Obama was focused on the nuclear threat from "non-state actors" and not the nuclear-armed North.

"The security of the world depends on the actions that we take," he said in a speech to delegates at the start of the day.

Obama in 2009 declared his vision of a world without nuclear weapons and the following year hosted a Washington summit, aimed at securing or destroying the world's stocks of plutonium and highly enriched uranium (HEU) by 2014.

"We are fulfilling the commitments we made in Washington. As a result, more of the world's nuclear material will never fall into the hands of terrorists who would gladly use it against us," Obama said.

"What's also undeniable is that the threat remains. There are still too many bad actors in search of these dangerous materials and these dangerous materials are still vulnerable in too many places.

"It would not take much -- just a handful of so of these materials -- to kill hundreds of thousands of innocent people."

But as a consequence of the Seoul summit, "more of our citizens will be safer from the danger of nuclear terrorism", Obama declared.

Highlighting the threat, an Interpol representative told the session there was "lots of evidence" that Al-Qaeda would use nuclear weapons if it had them, according to German delegation sources.

Interpol said there were 3,000 cases in 119 countries in which nuclear material had gone missing.

China's Hu, in his opening speech, noted good progress since 2010 but said the situation "remains grave".

He said his country would deepen cooperation with UN nuclear watchdog the International Atomic Energy Agency and help countries that want to convert reactors from HEU fuel to low enriched uranium.

Summit host, South Korean President Lee Myung-Bak, said the proliferation of nuclear weapons and the threat of nuclear terrorism "pose a grave challenge" to peace.

The world still has some 1,600 tons of HEU and 500 tons of plutonium -- enough to make more than 100,000 nuclear weapons, Lee said, calling for firm commitments to action.

Leaders were also tackling the threat posed by loosely-guarded radioactive material in hospitals and other sites, which could be combined with high explosives to make a "dirty bomb".

Late Monday France, Belgium, and the Netherlands -- three of the world's top suppliers of medical isotopes -- announced plans eventually to phase out the use of HEU in the production process, under a deal with the United States.