PHNOM PENH, Cambodia -- Cambodian Prime Minister Samdech Techo Hun Sen left here for Vientiane on Saturday to discuss border issue with his Laos counterpart Thongloun Sisoulith after issuing a six-day ultimatum to Lao troops to retreat from Cambodian territory, China's Xinhua news agency reported.

The Cambodian leader was accompanied by Foreign Minister Prak Sokhonn, Defense Minister Gen. Tea Banh, and Commander-in-Chief of the Royal Cambodian Armed Forces Gen. Pol Saroeun.

The country's foreign ministry said in a statement on Friday that Hun Sen "will ask the Laos government to withdraw all of its armed forces from the areas of O Alay and O Ta Ngav in Sieng Pang district in Stung Treng province bordering Laos' Attapeu province."

Hun Sen said on Friday that since April, Laos has sent about 30 soldiers to occupy the areas in Cambodia's northern Stung Treng province illegally under the pretext of preventing Cambodia from constructing a road along the border.

He said to maintain niceties, he ordered the engineering unit to halt the construction of the road, but the Lao troops have not pulled back.

"I send a message from here, calling on His Excellency Thongloun Sisoulith, the prime minister of Laos, to withdraw troops from Cambodian territory without any conditions," Hun Sen said during a ceremony in Phnom Penh. "The latest ultimatum is Aug 17."

Hun Sen said he has ordered his troops to be redeployed in Stung Treng province, and military action will be taken against those invading forces when the ultimatum comes.

On Friday night, the government-aligned media Fresh News live broadcast on its Facebook page from the prime minister's bodyguard headquarters in southern Kandal province, showing troops and dozens of armored vehicles and BM-21 multiple rocket launchers-carrying trucks departing for the border area in Stung Treng province.

Meanwhile, Kun Kim, deputy commander-in-chief of the Royal Cambodian Armed Forces, said some 5,000 soldiers equipped with machine guns and rocket launchers were also sent to Stung Treng province from nearby Preah Vihear province on Friday night, according to the Fresh News.

Cambodia shares about 540 km of border with Laos to the north and northeast. To date, the two neighbors have completed 86 per cent of the border demarcation.

Cambodia's last border clashes were with Thailand from 2008 to 2011 when Thailand claimed the ownership of 4.6 square km of scrub next to the Cambodia's ancient Preah Vihear temple.

In November 2013, the Hague-based International Court of Justice ruled that Cambodia had sovereignty over the whole territory of the promontory of Preah Vihear temple and ordered Thai soldiers to leave.