Japan says it will maintain sanctions on North Korea, despite Pyongyang's agreement to return to six-party talks about its nuclear weapons programme.
North Korea said its test was a "self-defensive measure"
Foreign Minister Taro Aso said the North's decision was welcome, but added that Japan would still demand that it give up all its nuclear activities.
Agreement to restart the discussions came at a meeting on Tuesday in China.
Pyongyang has now confirmed the news, saying it wants the talks to discuss the lifting of US financial sanctions.
"It is truly welcome that the talks are set to be resumed soon, but we cannot merely celebrate, saying 'That's great'," Japan's Kyodo news agency quoted Mr Aso as saying.
"We will continue to demand that North Korea give up all its nuclear weapons and existing nuclear programme."
After the North conducted its nuclear test on 9 October, the United Nations Security Council imposed new sanctions on the secretive nation.
Japan also imposed measures of its own, including a ban on all North Korean imports and a prohibition on its ships entering Japanese waters.
In the aftermath of the nuclear test, there was a flurry of diplomatic activity designed to bring the North Koreans back to the negotiating table.
KOREAN NUCLEAR CRISIS
Sept 2005: At first hailed as a breakthrough, North Korea agrees to give up nuclear activities
Next day, N Korea says it will not scrap its activities unless it gets a civilian nuclear reactor
US imposes financial sanctions on N Korea businesses
July 2006: N Korea test-fires seven missiles
UN Security Council votes to impose sanctions over the tests
Oct 2006: N Korea claims to have carried out nuclear test
Efforts were particularly focused on the Chinese, who have the most leverage on Pyongyang.
That pressure seemed to produce results on Tuesday when it was announced in Beijing that North Korea had agreed to return to the six-party discussions - which involve the two Koreas, the US, China, Japan and Russia.
Pyongyang confirmed its decision on Wednesday, adding that it would use the talks to seek the lifting of US financial sanctions. North Korea pulled out of the talks in 2005 in protest at Washington's decision to impose such sanctions.
North Korea's foreign ministry said Pyongyang had decided to return to the talks on the premise that the sanctions issue "will be discussed and settled between the DPRK (North Korea) and the US within the framework of the six-party talks".
As well as Japan, the other members of the six-nation talks all welcomed the decision to resume discussions.
US President George W Bush hailed the news, but added that it would not halt US efforts to enforce a UN Security Council resolution passed in response to the North's atomic test.
"We'll be sending teams to the region to work with our partners to make sure that the current United Nations Security Council resolution is enforced, but also to make sure that the talks are effective, that we achieve the results we want - which is a North Korea that abandons her nuclear weapons programmes and her nuclear weapons in a verifiable fashion in return for a better way forward for her people," he said.
N KOREA NUCLEAR PROGRAMME
Believed to have 'handful' of nuclear weapons
But not thought to have any small enough to put in a missile
Could try dropping from plane, though world watching closely
The six-party talks began in 2003 to find a way to resolve the crisis over Pyongyang's nuclear programme.
They appeared to make an historic breakthrough in September 2005 when North Korea announced it would give up its nuclear activities and rejoin the nuclear Non-Proliferation Treaty.
But within months, optimism crumbled as North Korea withdrew from the talks in protest at US financial sanctions, under which about $24m (£14m) of funds had been frozen.
North Korea's decision to test seven missiles in July and then carry out a nuclear weapon test on 9 October drew international condemnation.