Prime Minister Hun Sen yesterday wrote to three world leaders to request “cooperation” to secure copies of maps of Cambodia’s borders, which he said are held by the governments of France, the UK and the US.

The letters, addressed to US President Barack Obama, British Prime Minister David Cameron and French President Francois Hollande, request copies of the Bonne maps, which were recognised in the 1960s.

To Hollande, Hun Sen wrote that as “France produced the Bonne map . . . on the land borders between Cambodia and neighbouring countries, especially Vietnam, I would like your Excellency to provide a copy of this map”, adding that experts in cartography should attach verification notes to the document.

“My request is for the sake of Cambodia and its people . . . and to avoid and end the incitement to ultra-extremism that has caused confusion in national and international opinion.”

To Obama, Hun Sen said acquiring the maps was “an important undertaking for our sovereignty and the territorial integrity of Cambodia”.

He was aware that the US held a copy of the maps due to letters sent between foreign ministers in 1964, as well as a visit to the Library of Congress in 2003 and 2004, where the maps were viewed by Cambodian officials.

Cameron was asked about letters sent between the UK government and late King Father Norodom Sihanouk, which Hun Sen said indicated that Britain may also have been sent copies of the Bonne maps.

Speaking yesterday, Foreign Minister Hor Namhong told reporters that while a similar letter the premier had written to UN Secretary-General Ban Ki-moon earlier this month had yet to receive a reply, “through unofficial channels, we are told that they have not found the maps yet,” he said.