PHNOM PENH (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.

Cambodia's King Norodom Sihamoni (C) reads a document as he attends a senate meeting in Phnom Penh, Cambodia, April 23, 2018. REUTERS/Stringer

Prime Minister Hun Sen’s Cambodian People’s Party (CPP) won every seat up for grabs in the Feb. 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”.

CPP spokesman Sok Eysan did not reply to a Reuters request for comment.

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.

Last November, the Supreme Court dissolved the main opposition Cambodia National Rescue Party (CNRP) at the government’s request.

After the CNRP’s dissolution more than 5,000 opposition councillors and lawmakers were stripped of their voting rights, the CNRP said, paving the way for the CPP’s landslide victory.

“The formation of this ‘new Senate’ is just a part of the destruction of democracy in Cambodia, with the country painfully returning to a one-party system,” Sam Rainsy, the former CNRP opposition leader who lives in exile in France after he stepped down, said in a email to Reuters.

The CNRP was banned after Sam Rainsy’s successor, Kem Sokha, was arrested and accused of plotting to overthrow the government with help from the United States, accusations rejected by Washington and Kem Sokha, who is in prison.

The United States, which has spent more than $1 billion to support Cambodia, said after the Senate election it would curb military support and other aid programs due to “recent setbacks” in the country’s democracy.

The European Union has threatened Cambodia with economic sanctions and put a preferential trade agreement under review.

Hun Sen has said he will not tolerate any foreign criticism of Cambodia’s domestic politics and has said his actions aim to protect national security.