Hun Sen, who ruled Cambodia for nearly 33 years, took 'selfies' with supporters and enjoyed a boat ride following Sunday's election in which his Cambodian People's Party (CPP) said it had won all 125 parliamentary seats.
Although 20 parties contested the election, the only one with the popularity and organization to mount a real challenge, the Cambodian National Rescue Party, was dissolved last year by the Supreme Court in a ruling generally seen as political.
The White House said it would consider steps, including an expansion of visa restrictions placed on some Cambodian government members, in response to "flawed elections" in which there was no significant challenger to Hun Sen.
In power for 32 years, Hun Sen is already the world's longest-serving prime minister and among its longest-serving leaders. In 2007, he said he wanted to retire at age 90, but backtracked on the claim in 2015.
"It's the United States. It's an act of treason with conspiracy with foreign country, betraying his own nation, this requires arrest," Hun Sen said. Details of the alleged plot have not been made public.