North Korea's new leadership said Wednesday it would suspend nuclear and missile tests and its uranium enrichment programme as part of a deal that includes US food aid for the impoverished nation.

The agreement, confirmed simultaneously by Washington, represents a potential breakthrough in efforts to halt the North's drive for atomic weapons following the death of longtime leader Kim Jong-Il last December.

The deal followed talks in Beijing last week between the two sides, the first dialogue since Kim's young and untested son Kim Jong-Un took power.

A Pyongyang foreign ministry spokesman said Washington had promised 240,000 tonnes of "nutritional assistance", with the prospect of additional food aid for the North, which has suffered severe food shortages since a famine in the 1990s.

The North said it would allow the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), to monitor the moratorium on uranium enrichment.

The enrichment programme, first disclosed in November 2010, could give the communist state a second way to make atomic weapons in addition to its longstanding plutonium programme.

This is believed to have produced enough material for six to eight atomic weapons.

The North said the US side offered to discuss the lifting of sanctions and provision of light-water reactors to generate electricity as a priority, once long-stalled six-party nuclear disarmament talks resume.

The Beijing discussions were aimed at persuading the North to return to the six-nation talks which it abandoned in April 2009. It staged its second atomic weapons test a month later, following the first in 2006.

There were widespread reports in December that the two sides were close to such a deal, but the sudden death of Kim Jong-Il threw the process into uncertainty.

The new leadership headed by Jong-Un has taken a generally tough tone with the United States and South Korea, blasting joint military exercises which started on Monday as a rehearsal for war.

"The United States still has profound concerns regarding North Korean behaviour across a wide range of areas, but today's announcement reflects important, if limited, progress in addressing some of these," US State Department spokeswoman Victoria Nuland said in a statement.

US Secretary of State Hillary Clinton told US lawmakers the announcement "represents a modest first step in the right direction". The United States, she said, "will be watching closely and judging North Korea's new leaders by their actions."

IAEA chief Yukiya Amano called the deal "an important step forward" and Japan's Foreign Minister Koichiro Gemba welcoming it in similar terms. His country is a member of the six-party talks along with the two Koreas, host China, the United States and Russia.

The North said it "agreed to a moratorium on nuclear tests, long-range missile launches, and uranium enrichment activity at Yongbyon and (to) allow the IAEA to monitor the moratorium on uranium enrichment while productive dialogues continue".

It said both sides reaffirmed their commitment to a September 2005 six-nation deal. This envisaged the North scrapping its nuclear programmes in return for major diplomatic and economic benefits and for a peace treaty formally ending the 1950-53 Korean War.

In the 2005 deal, the six parties agreed to "respect" the North's desire for light-water reactors to generate electricity. Such reactors are less easily converted to military applications.

Washington-based North Korea expert L. Gordon Flake said the United States was eager for a cooling of tensions with North Korea before elections in November.

"In the context of a political year in Washington, the worst thing we could have when dealing with ongoing events in Syria and elsewhere is for North Korea to flare up," said Flake, executive director of the Mansfield Foundation.

Flake said the United States had probably already been prepared to provide North Korea with food aid based on humanitarian assessments.

"It appears to me that the North Koreans have agreed to a moratorium and inspections in return for something that we were already ready to give them, so it's a good deal for the US," he said.

Pyongyang, in a statement on its official news agency, said both sides recognised the armistice which ended the war as "the cornerstone of peace and stability on the Korean Peninsula until the conclusion of a peace treaty".

Nuland said the United States "reaffirms that it does not have hostile intent toward the DPRK (North Korea) and is prepared to take steps to improve our bilateral relationship in the spirit of mutual respect for sovereignty and equality".

She called for greater people-to-people exchanges.