PHNOM PENH, Cambodia — Khmer Rouge prison chief Duch will appeal against his conviction by Cambodia's UN-backed war crimes tribunal, which sentenced him to 30 years in jail, his defence lawyer said Tuesday.

Duch, whose real name is Kaing Guek Eav, was found guilty of war crimes and crimes against humanity by the court on Monday.

He is the first Khmer Rouge cadre to face an international tribunal over crimes committed under the 1975-1979 hardline communist regime.

The 67-year-old was initially handed 35 years but the court reduced the jail sentence on the grounds that he had been detained illegally for years before the UN-backed tribunal was established.

"We will appeal against the (court's) decision," Duch's lawyer Kar Savuth told AFP by telephone, without elaborating.

Many survivors and relatives of victims were dismayed by the verdict, which also took into account the years Duch had already served since his arrest in 1999, meaning that he could walk free in about 19 years.

"He only apologised to the judges. Duch didn't apologise to the victims," said Chum Mey, 79, one of the handful who survived the prison because his mechanical skills were put to use repairing sewing machines and water pumps.

During his trial, Duch repeatedly apologised for overseeing the mass murder of 15,000 men, women and children at Tuol Sleng prison -- also known as S-21 -- but shocked the court in November by finally asking to be acquitted.

Kar Savuth in November said Duch wanted to be acquitted on the grounds that he was not a senior member of the Khmer Rouge hierarchy, while his other defence lawyer Francois Roux had argued for leniency based on his contrition.

Prosecutors have said they are also considering whether to appeal the verdict. They had sought a 40-year prison sentence from the tribunal, which did not have the power to impose the death penalty.

But international co-prosecutor Andrew Cayley told AFP Tuesday he thought it was a "logical, well-reasoned judgement".

"You must recall that this is a man who actually acknowledged responsibility and pleaded guilty but still received a sentence of 35 years, which is actually on the high side as far as guilty pleas are concerned," Cayley said.

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