The six-party talks, which began in August 2003, bring together North Korea, South Korea, China, Japan, Russia and the US.
'Dastardly behaviour'
The North Korean foreign ministry official on Sunday accused Japan of using "obstructionist measures" against Chongryon, a group of pro-Pyongyang Koreans which serves as the North's de facto embassy in Japan.
Your Views

"North Korea has only one card in hand and that is its nuclear programme

Rahy, Tehran, Iran

Send us your views

The spokesman said Shinzo Abe, the Japanese prime minister, had persistently rejected Chongryon's proposals to clear its debts and taken harsh actions including forced entry and search, assaults and arrests.
"As Japan is behaving so dastardly with a black-hearted intention, the DPRK [North Korea] cannot but raise a serious question as to whether there is any need for its continued participation in the six-party talks," said the spokesman.
"The DPRK will never remain a passive onlooker to the Abe group's harsh suppression of Chongryon and its relevant field will take necessary steps against it."
Terms accepted
Meanwhile, Pyongyang agreed to UN verification procedures for the shutdown of its nuclear programme, inspectors from the International Atomic Energy Agency said on Tuesday.
The IAEA "will have access to all facilities and equipment that have been shut down and/or sealed for the purpose of monitoring and verification activities," a report on the terms said.
But with the latest threat to pull out of six-party talks, doubts have arisen about when actual disarmament would begin.
Plans to send in a new IAEA inspector mission will be authorised after a board meeting next week.
Mohamed ElBaradei, the IAEA director, recommended the same inspectors North Korea expelled more than four years ago to be assigned.
Pyongyang has already begun demanding promised shipments of oil before the shutdown.
US officials said on Tuesday they would not oppose releasing some of the 50,000 tonnes of oil promised.