Dinko Sakic, centre, commanded the Jasenovac concentration camp during the Second World War. He is shown listening to his verdict in Zagreb in 1999. (Antonio Bat/Associated Press)

The last-known living commander of a notorious Croatian Second World War concentration camp died early Monday morning while serving out a 20-year sentence for war crimes.

Dinko Sakic, who was chief of the Jasenovac camp where tens of thousands of Serbs, Jews, Roma and anti-fascist Croats were killed, died in a penitentiary hospital after a long illness that included heart problems, officials said in a statement.

He was 87 and had been convicted in 1999 by a court in Zagreb, the Croatian capital, for carrying out or condoning the torture and slayings of inmates while in charge of the Jasenovac camp in 1944.

Sakic fled his native country at the end of the war and was living unperturbed in Argentina until 1998, when he was extradited back to Croatia to face trial.

The camp he ran was known as the worst of about 40 operated by the Nazi puppet state that governed Croatia during the Second World War.

When Sakic was convicted, the judgment against him said that he had been responsible for mass and systematic torture, killings, inhuman treatment and terror.

Sakic never regretted his role in Jasenovac, defiantly claiming that all he did was for the good of Croatia and that "no harm was done" to the inmates. When he was given the guilty verdict at his trial, he mockingly applauded.

With files from the Associated Press