CAMBODIAN monarch King Norodom Sihanouk arrives in Hanoi tomorrow for the first time in 22 years in a bid to improve traditionally prickly ties with Vietnam. Senior sources said King Sihanouk - once considered stridently anti-Vietnamese - now wants to ensure future goodwill. 'In the current climate there should be no reason why we can't build and develop our ties,' one official said, referring to a history of turbulence and mistrust. 'We hope there is a feeling on both sides to look to the future.' Talks on a wide range of issues are likely to be overshadowed by reports of anti-communist groups of Vietnamese exiles planning to overthrow Hanoi from bases in Cambodia's capital Phnom Penh. King Sihanouk is labouring under a string of illnesses, and is thought to have lost a lot of his clout with Phnom Penh's coalition rulers, but he will travel with a delegation of key diplomats. Vietnamese back-room lobbying has ensured moves to deport leaders of the Free Vietnam movement and other groups from Cambodia. But doubts remain in Hanoi about full commitment to the drive. So far eight ringleaders have been arrested but some reports suggest the groups have created a growing political front with strong financial and moral ties to former South Vietnamese military exiles in California. 'The presence of such groups in Phnom Penh is very worrying and Vietnam will be seeking assurances every step possible is being taken,' one Hanoi source said. 'The worry is the knowledge that if there is one thing that can unite the troubled arena of Cambodian politics, it is anti-ethnic Vietnamese feeling.' Deep-seated hatred of ethnic Vietnamese is widespread in the country's ethnic Khmer population, despite many having lived in Cambodia for generations. Last year as many as 50,000 Vietnamese fishermen fled down the Mekong amid fears of violence from both provincial government officials and from Khmer Rouge guerillas. Vietnam wants many of the new migrants to return home, travelling up river to the traditional fishing villages on the Tonle Sap lake, far more productive waters than can be found in Vietnam. It is seeking further Cambodian assurances of their safety. Up to 35,000 people are now massed around the crowded tributaries of the Vietnamese side of the Mekong.