The decision technically removes all government officials from the military chain of command.

But, as Prime Minister, Hun Sen will remain in overall charge of the army and defence ministry.

General Ke Kim Yan was promoted from chief of staff to commander-in-chief at a ceremony in Phnom Penh on Thursday.

Hun Sen said the demise of the Khmer Rouge guerrilla movement, through a series of defections and surrenders, meant there was no longer a need for direct control of the army.

'End of war'

He said: "The disintegration of the Khmer Rouge political and military organisations has led to the end of war.

"There is no longer a need for direct command by the prime minister."

The last remnants of the Khmer Rouge rebel army surrendered to the government last month.

The group, under Pol Pot, was responsible for the deaths of more than one million Cambodians during its years in power between 1975- 1979.

One senior government official called Hun Sen's resignation a move to fight the country's international reputation as a state ruled by warlords.

Prince Sisowath Sirirath, a defence minister, said: "Hun Sen wants to show a new image of Cambodia."