They said Japan would only lift the measures, which include a ban on all North Korean imports, if Pyongyang abandons its nuclear programme completely.

"We still don't know the conditions" for North Korea's return to the talks, Foreign Minister Taro Aso told a parliamentary committee.

"We can't welcome the resumption of the six-way talks with open arms. Basically we will continue with the sanctions," he said.

North Korea said Wednesday it would return to the disarmament talks with South Korea, China, the United States, Japan and Russia on the condition that the issue of lifting US financial sanctions is settled during the negotiations.

The decision came just three weeks after the communist state stunned the world with its first atomic test.

Chief Cabinet Secretary Yasuhisa Shiozaki, the top government spokesman, said Japan will not lift its sanctions unless North Korea abandons all its nuclear programmes.

"Unless we are sure North Korea abides by (the UN Security Council resolution 1718 and the joint statement adopted at the six-nation talks in September last year), we will continue with the sanctions," Shiozaki said.

He said Japan would demand that the issue of Japanese civilians abducted by North Korea be taken up at the six-party talks.

Tokyo has demanded the North to come back to the table unconditionally.

The UN Security Council resolution, adopted against North Korea last month following its nuclear test, demands that Pyongyang abandon all nuclear weapons and existing nuclear programmes.

In a joint statement adopted in September 2005 at the six-party talks the North agreed to scrap its nuclear programmes in exchange for energy and economic benefits and security guarantees.

North Korea, which said on October 9 it tested its first atom bomb, walked out of the six-nation talks nearly a year ago to protest a set of US financial sanctions.

Shioichi Nakagawa, a close ally of Prime Minister Shinzo Abe and policy chief of the ruling Liberal Democratic Party, said Pyongyang's announced return to the six-party talks "doesn't mean the resolution of the problem."

"The announced return could be a means of earning time. North Korea is a diplomatically savvy country," Nakagawa told a news conference.

"North Korea is likely to say it is participating in the six-party talks as a nuclear power, but we can't accept that argument," said Nakagawa, who is among the politicians who has called for a debate on whether Japan should develop its own nuclear weapons in response to Pyongyang's test.

Japan imposed its own severe sanctions on North Korea after its nuclear test, halting all imports and all transport links.