North Korea has agreed to take the first steps towards nuclear disarmament, as part of a deal reached during six-nation talks in Beijing.
US envoy Christopher Hill says there is still a way to go
Under the agreement, Pyongyang has promised to shut down its main nuclear reactor in return for fuel aid.
The US and Japan have also pledged to begin talks with North Korea on building closer ties.
The agreement was read out in front of delegates at the close of the talks, by China's chief envoy Wu Dawei.
Mr Wu said the deal was "favourable for the peace process in north-east Asia and for the improvement of ties between relevant countries".
White House spokesman Tony Snow called it "a very important first step" towards denuclearising the Korean peninsula.
Delegates from the two Koreas, the US, China, Japan and Russia had been meeting in Beijing since Thursday.
They worked late into Monday night to try and hammer out the final details of the deal.
Under the agreement, Pyongyang has pledged to close its Yongbyon reactor within 60 days, in return for 50,000 metric tons of fuel aid or economic aid of equal value.
The closure of Yongbyon will be verified by international inspectors.
The North will eventually receive another one million tonnes of fuel oil or an equivalent when it permanently disables its nuclear operations.
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The US has agreed to begin the process of removing North Korea from its list of terror states and establish diplomatic relations.
Japan will also discuss normalising relations with the North.
Chief US negotiator, Christopher Hill, said the agreement reached this week was "only one phase of denuclearisation. We're not done."
One of the topics that looks set to be left for later discussion is the fate of any nuclear weapons the North already possesses.
Signs of progress
In Washington, Mr Snow hailed the deal but sounded a note of caution.
"If they don't abide by the terms, they don't get the benefits they desire," he said.
"There's still the possibility of sanctions through the international community."
Other US figures had earlier voiced scepticism.
John Bolton, former US ambassador to the United Nations, said North Korea should not be rewarded with "massive shipments of heavy fuel oil" for only partially dismantling its nuclear arsenal.
"It sends exactly the wrong signal to would-be proliferators around the world," Mr Bolton told CNN.
And while Japan has approved the joint agreement, Foreign Minister Taro Aso was quoted as saying that Tokyo would not provide aid as there had been no progress on the issue of Japanese nationals abducted by the North in the 1970s and 80s.
But despite the difficulties ahead, analysts say this deal is an important sign of progress, after more than three years of talks.
The previous deal, agreed in September 2005, rapidly fell apart over differences between North Korea and the US over implementation.
The North Korean nuclear issue has become even more pressing in recent months, after Pyongyang conducted its first atomic test in October.