PHNOM PENH, Dec. 29 -- An estimated 40,000 opposition supporters took to the streets in capital Phnom Penh Sunday afternoon to demand the resignation of Prime Minister Hun Sen and a re-vote following allegations of serious irregularities during the July election.

It was the 15th day of the opposition's daily protests and was the largest-ever since the disputed July poll because thousands of protesting garment workers, who have gone on strikes since Wednesday over low wage hike, have also taken part in the opposition's protests.

Most of the protesters were trucked from the countryside to join the protests. Many of protesters tied ribbons around their heads carrying slogans such as "We need a reelection," "Hun Sen must step down," "Long live democracy!"

Security forces have been seen deployed along streets and government buildings to ensure security and public order.

Addressing to the rally at the Freedom Park before marching through streets in the capital, Sam Rainsy, president of the opposition Cambodia National Rescue Party, said: "Political tsunami has come again and a huge number of people have participated in this protest."

Political dispute between Hun Sen's ruling party and 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.

Premier Hun Sen, who has ruled the country for 28 years, said on Dec. 20 that he would neither step down nor hold a reelection because he had done nothing wrong.

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

Political analysts proposed that Cambodia should hold a referendum to decide whether the country calls a reelection or not after allegations of serious irregularities during the July election.

Kek Galabru, president of a renowned human rights group Licadho, said that a referendum could be the best way to break through the five-month-old political dispute in Cambodia.

"In my opinion, the leaders of the two parties are the same Khmers. If they have the same good will and want to serve the interest of the nation and the people, they should sit down and talk to find ways to resolve the differences," she told Xinhua on Saturday.

"In a democratic society, people are the owners of the power. The two leaders should ask the people through a referendum whether they want a reelection or not. If a majority of them want a reelection, they must follow the will of the people."

She envisaged that without a referendum or a re-vote, the political crisis could lead the country into political instability and economic depression.

"The opposition's daily protests are causing social instability and discouraging investors and tourists to Cambodia," she said.