Thirty officials of the North Korean regime who were involved in talks with South Korea have been executed or died in "staged traffic accidents," according to a human rights report.

In its annual study, Amnesty International claimed that in addition to the 30 who died in purges last year, a further 200 were rounded up in January this year by the State Security Agency as Pyongyang carried out the transfer of power from Kim Jong-il, who died of an apparent heart attack in December, and his 29-year-old son, Kim Jong-un.

Of those 200, Amnesty said, some were apparently executed and the remainder were sent to political prison camps. The gulag system presently contains an estimated 200,000 people in "horrific conditions," the group said.

North Korea has a habit of executing bureaucrats who are perceived to have failed the regime, even though they are often merely carrying out the orders of higher-ranking officials or members of the ruling family.

In 2010, Pak Nam-gi, the former head of the finance department of the Workers' Party, was reportedly executed by firing squad for the catastrophic attempt to reform the impoverished nation's currency. The result was rampant inflation and food shortages became even more acute.

The 30 men executed for failing to improve Pyongyang's ties with Seoul are considered scapegoats for the new low point in inter-Korean ties.

Their task would have been made immeasurably more difficult given North Korea's insistence with pushing ahead with its development of nuclear weapons and intercontinental ballistic missiles.

In spite of universal condemnation of its failed attempt to launch what Pyongyang claimed was a rocket to put a satellite into orbit in April, North Korea appears to be putting the finishing touches to a test detonation of a nuclear device.

Kim Min-seok, a spokesman for South Korea's Ministry of Defence, said on Thursday that intelligence reports indicate the North has completed its technical preparations to carry out the long-awaited test and that it could go ahead at any time.

Satellite images of the Punggye-ri site and other data show that the tunnel that had been excavated for the test has been refilled, indicating that the nuclear device has been put in place.

There is speculation that the test may be timed to coincide with the Memorial Day national holiday in the United States, which falls in Monday.

"The North Korean regime is hell-bent on being a belligerent actor," said Ileana Ros-Lehtinen, chair of the US House Foreign Affairs Committee, during a visit to Seoul with a congressional delegation. "And I think that on holidays or sad commemorations like Memorial Day weekend is when the leadership tries to provoke the democratic allies into action."