Cambodia's prime minister has said that no state officials were to blame for a stampede last week that killed 351 people and ruled out resignations in the aftermath of the country's worst tragedy in three decades.

Prime Minister Hun Sen has said that calls for senior figures within the government and security forces to step down were politically motivated to serve opposition parties, but he said mistakes had been made and the situation was badly handled.

The stampede caused the biggest loss of life since the Khmer Rouge regime's four-year reign of terror in the late 1970s, during which an estimated 1.7m Cambodians died from execution, disease, starvation and exhaustion.

The incident happened late last Monday when more than 1,000 people celebrating the end of an annual Water Festival on a man-made entertainment island crossed a narrow bridge.

The crowd suddenly panicked and started to run.

'The incident happened because of carelessness and we didn't expect this thing to happen,' he added. 'The biggest mistake was that we had not fully understood the situation.'

The victims died mostly of suffocation, while some drowned after leaping into the Tonle Sap river below.

Mystery surrounds what triggered the stampede, with varying witness accounts.

The Cambodian government said in a preliminary report last week that the Diamond Gate bridge moved slightly under the weight of people, who thought it was about to collapse.