Cambodia and Vietnam are in the process of demarcating their shared border, and the placement of some markers has proved contentious with claims they encroach on Cambodian farmers' fields.

Sam Rainsy Party lawmaker Son Chhay said the legislators had heard that the border marker was well inside Cambodian territory and went to inspect it but more than a dozen military police tried to prevent them from reaching the site.

"If the government has nothing to hide, they should not work so hard to stop us 5 kilometres away," he said by telephone.

The group eventually managed to get within 150 metres of the post in the south-eastern province of Takeo before they were again turned back by local police.

The government on Tuesday warned that the trip was illegal and said it would prevent the group from reaching the area.

Opposition leader Sam Rainsy was sentenced in absentia in January to two years jail for his role in uprooting boundary posts in October on the Vietnam border.

That incident riled Hanoi, which has close links to the government in Phnom Penh.

Vietnam also has significant business interests in Cambodia, including investments in agribusiness, aviation, telecommunications and banking.

Deutsche Presse Agentur - June 3, 2010