PHNOM PENH, April 23, 2018 (Reuters) - Cambodia's King Norodom Sihamoni on Monday urged senators to protect justice and human rights as the upper house of the country's parliament met for the first time since the ruling party swept a controversial election in February. Prime Minister Hun Sen's Cambodian People's Party (CPP) won every seat up for grabs in the February 25 election after many opposition supporters were stripped of the right to vote late last year. Rights groups and opposition leaders called the vote a "sham" and "undemocratic", while Western governments have suspended aid and some imposed sanctions, including travel curbs, on senior CPP members. "The Senate has to guarantee to protect justice and human rights in order to improve happiness in our society," the king said in a speech on Monday congratulating the newly-elected lawmakers. He reminded them of the Senate's duty to "protect basic constitutional rights and democracy, as well as the freedom and interests of all people". The CPP won 58 of the 62 Senate seats, which include two members each appointed by the king and the National Assembly. The four appointees are members of the royalist Funcinpec party of Prince Norodom Ranariddh, who was once Hun Sen's main rival but is now aligned with the prime minister.