Prime Minister Hun Sen's ruling Cambodian People's Party (CPP) said on Monday it had won all 125 parliamentary seats up for grabs in a general election a day earlier that critics said was neither free nor fair.

"The CPP won 77.5 percent of the votes and won all the parliamentary seats," CPP spokesman Sok Eysan told Reuters by telephone. "The other parties won no seats."

Cambodia woke to another chapter of rule by strongman Hun Sen on Monday, a day after an election that was heavily criticized by rights groups, the United States and other Western countries.

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.

Critics say the election was a backward step for democracy in Cambodia following the dissolution last year of the main opposition Cambodian National Rescue Party (CNRP) and the jailing of its leader, Kem Sokha, on treason charges.

Former CNRP president Sam Rainsy, who lives in exile, said the election was a "hollow" victory for Hun Sen, a former Khmer Rouge commander who has ruled Cambodia for nearly 33 years.

The United States has imposed visa curbs on some Cambodian government members over a crackdown on critics and levied sanctions in June on a high-ranking official close to Hun Sen.

The European Union has threatened Cambodia with economic sanctions. White House Press Secretary Sarah Sanders said in a statement Sunday's vote "failed to represent the will of the Cambodian people".

"The flawed elections, which excluded the country's principal opposition party, represents the most significant setback yet to the democratic system enshrined in Cambodia's constitution," Sanders said. The election campaign was marred by threats from national and local leaders, she said.

"The United States will consider additional steps to respond to the elections and other recent setbacks to democracy and human rights in Cambodia, including a significant expansion of the visa restrictions announced on December 6, 2017," Sanders said.

Government spokesman Phay Siphan said the White House statement was an attempt to intimidate Cambodia. "This is against the Cambodians who went to vote to decide their own fate," Phay Siphan told Reuters.