Devillers was arrested June 13 in Phnom Penh at the request of China, Cambodian officials said.
The report noted ongoing corruption at all levels of government, which thwarts efforts to crack down on trafficking.
Patrick Devillers, 52, reportedly lives in Phnom Penh and owns land in the coastal town of Kep.
The independent monitoring organization counted 3,000 irregularities at 5,810 polling stations in last month’s local elections.
A rights activist said Friday an investigation into the killing of environmental activist Chut Wutty in April had made some progress.
Cambodia will host a major Asean ministerial meeting in July, where Clinton is expected to attend.
Hun Sen announced a ban on May 7, but since then, the Ministry of Agriculture granted land to companies in three provinces.
The report said the vehicles were transported on a Cambodia-registered ship.
Foreign Minister Hor Namhong said after the meeting the Cambodia was seeking greater US investment in Cambodia.
Sam Rainsy Party officials said he was being arrested because of his politics and called for his immediate release.
A group of the protesters gathered in front of the Royal Palace for the second time on Monday.
The Cambodian People’s Party swept the commune elections on Sunday, winning nearly 1,600 of 1,633 commune chief positions.