PHNOM PENH (Reuters) - Forty-five countries called on Cambodia on Wednesday to reinstate the main opposition party, release its jailed leader and ensure a July general election is free and fair.

Slideshow ( 2 images )

A statement on the human rights situation in Cambodia read by New Zealand on behalf of a group of 45 countries, including the United States, Germany, Australia and United Kingdom, said previous optimism had been “replaced by deep concern” regarding a decline in civil and political rights in Cambodia.

The statement, which was read to the United Nations Human Rights Council in Geneva, urged Cambodia’s government to reinstate the opposition Cambodian National Rescue Party (CNRP) and all elected members.

Dozens of opposition lawmakers were banned when Cambodia’s Supreme Court dissolved the CNRP last year in a ruling that was widely condemned by the international community.

That decision followed the arrest of CNRP leader Kem Sokha last September. Kem Sokha has been charged with treason, accused of colluding with Americans to overthrow the Cambodian government. He denies the charges and the U.S. embassy in Phnom Penh has also denied the accusation.

Kem Sokha faces 30 years in prison if convicted.

Prime Minister Hun Sen has ruled Cambodia for 33 years.

He is a former Khmer Rouge cadre who defected from the genocidal group and helped drive it from power in 1979, and is credited with helping Cambodia achieve economic growth, but has been criticized for his crackdown on critics and the media.

“We call on the Royal Government of Cambodia to take all measures necessary, before it is too late, to ensure that the 2018 elections are free, fair and credible,” the statement said.

“We are particularly concerned about the conditions under which opposition leader Kem Sokha is being detained following his arbitrary arrest: he is reportedly in isolation, without adequate access to health care, subjected to intrusive observation, and other conditions, such as constant light.”

“We call for the immediate release of all political prisoners, including Kem Sokha.”

The group raised concerns about a government crackdown on freedom of expression that has extended to independent media and non-governmental organizations.

Government spokesman Phay Siphan said Cambodia won’t comply with demands made by foreign countries.

“We are equally members of the United Nations,” Phay Siphan told Reuters. “This is a violation of Cambodia’s sovereignty.”

“We will hold elections according to what Cambodians want, based on Cambodian laws,” he added.