The Cambodia National Rescue Party has asked Interior Minister Sar Kheng to ensure that Cambodians living near the border with Vietnam are barred from renting land to Vietnamese nationals.

It follows the CNRP’s demand earlier this week that the ministry send it a list of foreigners granted citizenship so its officials can check for irregularities.

The opposition has long complained of border encroachment by Vietnam and has previously alleged that illegal immigrants were able to vote in Cambodia’s elections. Last year its lawmakers launched a sustained campaign accusing the government of mismanaging its eastern frontier, and even carried out multiple controversial trips to border areas.

In a letter dated August 23 and signed by five opposition parliamentarians, the CNRP said it had uncovered several cases in Svay Rieng province in which 500 hectares had been leased to Vietnamese farmers.

The CNRP called on Sar Kheng to “take measures” to enforce a directive announced by Hun Sen, who in January said he had made a deal with his Vietnamese counterpart to stop the rental of land.

Interior Ministry spokesman Khieu Sopheak said that, when received, the letter would be considered, though he noted the premier’s directive was not law. “There are only the educational measures now,” he said of the ministry’s attempts to dissuade villagers on the border from leasing their land to Vietnamese nationals.

A perennially sensitive issue, border violations made headlines again last week when the Ministry of Foreign Affairs issued another diplomatic protest against Vietnam’s building of structures within zones that are not yet demarcated.

The issue was yesterday seized upon by the minor Cambodia Youth Party whose director, Pich Sros, revealed plans to petition the Vietnamese Embassy in Phnom Penh for a response. If none was forthcoming, he warned via Facebook, the group would lead a protest outside the embassy to “demand . . . an end to the violations”.

Sopheak agreed that Vietnam had “rudely” ignored Cambodia’s appeals, though he said the state’s priority was to maintain stability on the border.

Meanwhile, the CNRP’s second request – to receive a list of foreign nationals who have been granted citizenship – was on Wednesday forwarded to Sar Kheng. The letter followed comments by the National Election Committee that it would register any voter with an identity card whether or not they could speak Khmer.

The CNRP said it was seeking the lists to allay suspicions about the “number of illegal immigrants receiving IDs through corruption or any negligence of the Interior officials”.