The first day of Cambodian opposition\'s mass protest over the contested election results ended Sunday evening with clashes between police and protestors, injuring one police officer, a spokesman said. The peaceful demonstration turned violent in the afternoon when hundreds of protestors attempted to remove police\'s barbed wire barricades in order to march through a street in front of the Royal Palace. \"Police had fired tear gas and water cannons to disperse about 500 protestors as they removed the barbed wire barricades and threw stones at the police,\" National Military Police spokesman Kheng Tito told Xinhua after the clashes. \"One police officer got injured on his head due to a stone thrown by protestors.\" The clashes ended when Phnom Penh Municipal Police chief Chuon Sovann and opposition party leader Sam Rainsy arrived at the scene and held a talk. Speaking to his supporters via a microphone after the talk, Sam Rainsy said: \"We hold a peaceful protest; we condemn anyone who throws stones at the police.\" Then he led protestors to march back to the Freedom Park. Chuon Sovann said the use of tear gas and water cannons over the protestors was police\'s self-defense rights. The protest, organized by the opposition Cambodia National Rescue Party (CNRP) of long-time Sam Rainsy, aimed to reject the July 28 election results that showed the ruling Cambodian People\'s Party (CPP) of long-serving Prime Minister Hun Sen got victory with 68 parliamentary seats and the CNRP received the remaining 55 seats. The CNRP claimed that its party should win 63 seats, with the CPP getting 60 seats if alleged irregularities during the poll were fairly investigated. Sunday\'s protest started when Sam Rainsy led over a thousand of supporters to march from his party\'s headquarters in the southern part of the city to the Freedom Park in the morning. Security has been tightened throughout the city on Sunday as barbed wire barricades have been placed across major roads. At the Freedom Park, Sam Rainsy told about 20,000 supporters that the party would boycott the opening session of the parliament on Sept. 23 if there was no a proper solution to the alleged irregularities during the election. He said the mass protest would last for three days as makeshift tents had already set up at the Park for protesters from provinces to sleep at nights. After his speech, he led thousands of protestors marched on streets in the city. The opposition\'s protest came a day after a meeting between Sam Rainsy and Prime Minister Hun Sen under the auspices of King Norodom Sihamoni had reached no any agreement over the election impasse. However, the two political rivals would meet again on Monday at the National Assembly in a last-ditch attempt to break through the political stalemate, the two parties said. Prime Minister Hun Sen has said that his party has enough lawmakers to override any opposition parliamentary boycott and form a new government. Hun Sen, 61, who has been in power for 28 years, will rule the country for another five years through the election victory.