PHNOM PENH (AFP) - Cambodia's opposition said on Thursday that it had filed a lawsuit against the kingdom's poll authorities over strongman Prime Minister Hun Sen's disputed election win.

The Cambodia National Rescue Party (CNRP) accused three top National Election Committee (NEC) officials and their accomplices of faking voter names on the electoral roll, using "fake election results" and abusing the election law.

"These are criminal offenses," senior CNRP official Kuy Bunroeun told AFP after the lawsuit was filed at the Phnom Penh Municipal court.

"We are filing a complaint to find justice for the people," he added. "The results are not acceptable."

According to final results released by the NEC on Sunday, Mr Hun Sen's Cambodian People's Party (CPP) won 68 seats in the July polls against 55 for the opposition.

The CNRP has rejected the result, alleging widespread vote rigging, but so far its efforts to challenge the results have failed and it has few options left in its bid to overturn Mr Hun Sen's victory.

A mass rally in the capital on Saturday called for an independent probe into results, and further protests are planned in Phnom Penh for September 15, 16 and 17.

The opposition has also threatened to boycott parliament when it is convened by the king, which is expected to take place on September 23.

NEC secretary-general Tep Nytha, one of the officials being sued, said the poll body would cooperate in the case.

"It is their right to file a complaint and it is the right of the court to decide in the case. The NEC is ready to follow the court procedures," he told AFP.

Mr Hun Sen, 61, a former Khmer Rouge cadre who defected and oversaw Cambodia's rise from the ashes of war, has vowed to rule until he is 74.

His government is regularly accused of ignoring human rights and suppressing political dissent.