CAMBODIA vowed yesterday to smash groups it said were using Phnom Penh as a base from which to plot the overthrow of Vietnam's communist government. Cambodian Foreign Minister Ung Huot said the activists were a 'clear threat' to improved ties with Vietnam. 'We have told the Vietnamese we will drive them [the groups] from our country in the interests of good relations,' Mr Ung said. 'We think we have got rid of the American-Vietnamese leaders but we will keep going. 'We are proud to have built an honest, neutral state and we cannot allow it to be seen as an agent of instability . . . against Vietnam or for any other country.' Mr Ung arrived in Hanoi yesterday to guide Cambodia's King Norodom Sihanouk through his first visit to Vietnam in 22 years. The emergence of Vietnamese plotting the downfall of Hanoi from Phnom Penh is likely to underscore wide-ranging talks aimed at boosting ties between Hanoi and the country it dominated for most of the 1980s. At least six America-Vietnamese linked to a group calling itself Free Vietnam have been rounded up in recent weeks. The organisation has built a pro-democracy political wing and is said to have armed itself through links to exiled officers in the defeated South Vietnam army. Mr Ung said all leaders would be deported following investigations that took more than a year. When asked why Cambodia had taken so long to act, he said Phnom Penh had to be sure because it wanted to avoid charges that it was 'lawless dictatorship'. He refused to comment as to whether police were still investigating. Mr Ung said his key hope was for the royal delegation to secure a new era in relations with Vietnam, whose army invaded in 1979 to drive out its former comrades, the Khmer Rouge. King Sihanouk repeatedly urged Vietnam's military and other 'colonial' officials to leave in the years that followed, softening his line after United Nations-sponsored elections in 1993. The vote was followed by a new Constitution which restored the monarchy's power. Mr Ung refused to be drawn on concerns within Cambodia over the high-profile role of Second Prime Minister Hun Sen, a former Khmer Rouge officer previously installed by Hanoi. 'This visit more than anything else is about closing the door on the past,' Mr Unq said. 'I don't want to talk about the previous book, let's look ahead and open a new chapter. The relationship is good, but as we are so close, we believe it should get much better.'