The opposition party in Cambodia has rejected the results of the country's national election, which handed another win to long-serving Prime Minister Hun Sen. The Cambodia National Rescue Party (CNRP) said Monday the weekend balloting was marred by irregularities, and demanded an investigation. Cambodians went to the polls Sunday, CNN reported. According to preliminary results released by the national election commission, the opposition won 55 seats. But the number wasn't large enough to unseat the ruling Cambodian People's Party, which won 68 seats. In a statement, opposition leader Sam Rainsy said a committee -- made up of representatives of the main political parties, the election commission and foreign election monitors -- should look into "all serious election irregularities." Hun Sen has been in office for 28 years.