Cambodian King Norodom Sihamoni will convene the first National Assembly session on September 23 after the official election results were confirmed Sunday that Prime Minister Hun Sen's ruling party won an absolute majority of vote.

"I will invite all elect-lawmakers in the fifth legislature of the National Assembly for the first session on Sept. 23 at the National Assembly Palace," the King said in a royal message to Im Suosdey, president of the National Election Committee (NEC), on Monday.

Sihamoni has been in Beijing since August 12 for a routine medical checkup and is scheduled to return on Wednesday.

The NEC released the final election results on Sunday, showing that the Cambodian People's Party (CPP) of Prime Minister Hun Sen got 68 seats and the Cambodia National Rescue Party (CNRP) of long- time opposition leader Sam Rainsy took the remaining 55 seats.

But the opposition rejected the results, claiming that its party should win 63 seats, with the CPP receiving 60 seats if alleged irregularities during the poll were fairly resolved.

The CNRP said it would call a massive non-violent protest for three consecutive days starting on Sept.15 at the capital's Freedom Park and it would boycott the first session of the National Assembly if an independent probe committee was not formed to look into alleged poll irregularities.

"There will be a series of demonstrations. They will be larger because we will mobilize people who are not happy with the results of the election," Sam Rainsy told a press conference on Sunday. " The peaceful protests could last for days--both at daytime and nighttime."

The ruling CPP has repeatedly ruled out the opposition's request for an independent poll probe committee, saying it is against the country's constitution since the opposition has asked for the exclusion of the NEC from the proposed committee.

"There is no need to discuss the so-called independent poll probe committee since the official election results were released already," CPP's senior legislator Chheang Vun said Sunday.

Prime Minister Hun Sen has said that his party has enough lawmakers to override any opposition parliamentary boycott and form a new government.

He said that under the constitution, a new government would be formed by a 50- percent plus one majority, or 63 lawmakers, in the new parliament.

Hun Sen, 61, who has ruled the country for 28 years, will stretch his power for another five years through the victory.

Security forces and armored vehicles have been deployed around the capital since early last month after the opposition has repeatedly threatened to call mass demonstrations.