KAMPOT, Cambodia : A chartered tourist plane that disappeared in Cambodia likely crashed in bad weather, officials said Tuesday as more than 1,000 rescuers continued to scour dense forests for the wreck.

All 22 people on the aircraft -- 13 South Koreans, three Czechs, a Russian pilot and five local crew -- travelling from the Angkor temple town of Siem Reap to the seaside resort of Sihanoukville were feared dead, officials said.

The Russian-made AN-24, which disappeared from radar about 40 minutes after leaving Siem Reap early Monday, is thought to have crashed in the mountains of southern Kampot province, about 50 kilometres (30 miles) from its destination.

Cambodia's military commander-in-chief General Ke Kim Yan said an initial investigation showed that bad weather, rather than a mechanical failure, had likely brought the plane down.

"Our first evaluation of the cause of the plane crash is bad weather," he said, adding that poor visibility had forced the aircraft to divert through the mountains.

Ly Thuch, deputy director of Cambodia's National Disaster Committee, said more than 1,000 police, soldiers and local conservation workers were searching for the plane, but said they had only vague eyewitness accounts to guide them.

Rain also hampered rescue efforts, forcing those on the ground to trek along kilometres (miles) of muddy trails.

Three helicopters joined the search effort at mid-day after spending the morning grounded by heavy rain, military officials said, but fog and clouds limited their efforts.

"We hope to find them soon. The (rescuers) will search deeper into the forest," Ly Thuch said.

He said Cambodia had asked the US embassy to provide satellite photographs of the area to help them locate the crash site, as well as forensic experts, as hopes of finding any survivors were dimming.

"I hope there are some survivors, but nobody is sure," said South Korean Ambassador Shin Hyun-suk, before joining other Korean diplomats and Cambodian officials at a meeting called to map out how best to reach the crash site.

"The rain is affecting the search," he told AFP.

Prime Minister Hun Sen, who arrived in Kampot on Tuesday, offered 5,000 dollars to anyone who located the crash site.

"Even though only a small number of people died, it is a big disaster for Cambodia," he said earlier in Phnom Penh.

"We must find the dead bodies and send them back to their families ... We have little hope that those people are still alive, but we must try our best to help them."

South Korean diplomats told AFP they had identified all 13 Koreans on board, including two boys aged two and seven years old. All had been part of a tour group, they said.

South Koreans made up the largest percentage of 1.7 million foreign visitors to Cambodia in 2006.

The crash is the first major air disaster to strike Cambodia in a decade, but highlights the country's need to bolster domestic air safety amid a rise in tourist arrivals.

The plane was operated by Progress Multi Transportation (PMT) Air, which runs mainly domestic flights. It has had at least three accidents or in-flight emergencies in the past two years, and was temporarily grounded at one point.

PMT opened a route between Siem Reap and Sihanoukville in January. It also flies between Siem Reap and Seoul, according to its website.

South Korea's ministry of construction and transportation has called for PMT's fleet to undergo safety checks.

Cambodian Tourism Minister Thong Khon said other foreign-owned airlines considering whether to enter the market here "should be careful ... before they start flying in order to be as safe as possible."

"This could have happened anywhere in the world, not just Cambodia," he added.

Cambodia's last significant air accident occurred in 1997, when a Vietnam Airlines flight from Ho Chi Minh City to Phnom Penh crashed in heavy monsoon rain as it attempted to land at the capital's international airport.

Sixty-four people were killed in the crash. Only two infants, a Thai boy and a Vietnamese boy, survived.

- AFP