Cambodia's ruling party lawmakers said the opposition's calls for Prime Minister Hun Sen's resignation and a re-vote are a "clear and undeniable act of coup" against the current legitimate government, according to a statement released to the media on Monday.

The opposition Cambodia National Rescue Party (CNRP) has launched a new round of daily protest in capital Phnom Penh since December 15 in order to demand Hun Sen to step down or to call a snap election following allegations of serious irregularities during the July election.

On Sunday afternoon, an estimated 20,000 protesters, led by CNRP's President Sam Rainsy and his deputy Kem Sokha, took to the streets in the capital and shouted in chorus "Hun Sen must step down."

"Immoral and outlawed language used by Sam Rainsy, Kem Sokha and their accomplices to demand Premier Hun Sen to step down and call a reelection by early 2014 is a clear and undeniable act of coup," said the statement signed by 42 ruling party lawmakers.

The statement said the opposition's non-stop protests since December 15 are illegal and have violated the Demonstration Law.

CNRP's lawmaker-elect Ho Vann denied that the party's daily protests are trying to stage a coup against the Hun Sen's government.

"We are just holding peaceful protests to demand a re-vote. This is the norm in democratic countries," he told Xinhua over telephone. "It is not a coup attempt because all protesters have not used any weapons."

Sam Rainsy announced to his supporters on Sunday that " political tsunami" has begun in Cambodia and it would be the biggest of all on Sunday, Dec. 29.

Hun Sen said last Friday that he would neither step down nor call a re-vote because he has done nothing wrong.

The premier also warned to take legal action against protesters if they blocked highways or captured government buildings.

Political dispute between the Hun Sen's ruling party and the Sam Rainsy's opposition party has persisted since the July election results showed that the ruling party won a majority of vote with 68 parliamentary seats against 55 seats for the opposition.

The opposition refused to accept the outcome and has boycotted parliament since then.

Despite the opposition's boycott, the ruling party-formed parliament voted on Sept. 24 for the establishment of a new government under the leadership of Hun Sen.