A New Zealand man whose brother was killed by the Khmer Rouge in Cambodia is preparing to enter a court battle against two former senior members of the regime.

Rob Hamill's brother Kerry was tortured and killed at a prison in Phnom Penh in 1978, after the yacht he was on strayed into Cambodian waters.

Mr Hamill went to Cambodia last year to watch the United Nations-backed Extraordinary Chamber of the Courts convict the prison chief.

However he says a case against five other men has stalled, so he is filing an application to join it as a civil party, to prevent it being "quietly swept under the carpet."

Rob Hamill says his application focuses on two of the men, who he says had a pivotal role in his brother's death.

He says they work for the Cambodian government, which does not want them prosecuted.