Lawmakers from the Sam Rainsy Party (SRP), whose leader lives in exile in France, urged Prime Minister Hun Sen to allow a review of border markings to "properly and fully respect the territorial integrity of Cambodia".

The Cambodian premier maintains close relations with the Vietnamese regime and Sam Rainsy, whose party shares his name, has repeatedly accused the government of ceding land to Vietnam.

"We, the lawmakers... would like to request the government to suspend the process of planting markers along Cambodian-Vietnamese border," the letter said.

The move follows a government lawsuit filed last month against Sam Rainsy accusing him of publishing a false map on his party's website that disputed delineation of the border between Cambodia and Vietnam.

The opposition leader was in January sentenced in absentia to two years in prison in Cambodia for intentionally uprooting temporary border posts and inciting racial unrest.

Two villagers were also found guilty in the October incident in which Sam Rainsy led protesters to uproot six border markers in southeastern Svay Rieng province, alleging they had been illegally placed by Vietnam.

Vietnam condemned the saboteurs' act as "perverse, undermining common assets, violating laws of Cambodia and Vietnam, treaties, agreements and deals between the two countries".

But the SRP's letter to Hun Sen on Tuesday asked that independent experts, lawmakers, journalists, and civil society representatives be allowed to monitor and verify the demarcation process between the two countries.

Cambodia and Vietnam officially began demarcating their contentious border in September 2006 after decades of territorial disputes.

Anti-Vietnamese sentiment in Cambodia is rife, fuelled by resentment at Vietnam's expansion over the centuries and the feeling that Cambodia is losing some of its territory.

Vietnam and Cambodia share a 1,270-kilometre (790-mile) border, which has remained vague since French colonial times.