Cambodia's Prime Minister Hun Sen attends a press conference after the 10th Cambodia-Laos-Vietnam summit as part of the Greater Mekong Subregion Summit in Hanoi, Vietnam March 31, 2018. REUTERS/Kham/Pool

PHNOM PENH (Reuters) - Cambodia on Wednesday invited foreign observers to monitor a July general election, as required by law, which long-serving Prime Minister Hun Sen is poised to win after the main opposition party was dissolved.

The National Election Committee said the foreign observers would have to submit written reports on their findings.

Koul Panha, director of the Committee for Free and Fair Elections in Cambodia, an election watchdog, said international observers should think before accepting.

“They should be more cautious in responding to the invitation. Many of them have standards on prerequisite principles for their engagement decision,” he said.

Hun Sen and his supporters have waged a campaign against critics, including members of the opposition Cambodia National Rescue Party (CNRP), in what opponents say is a bid to prolong his leadership after 33 years in office.

The CNRP was dissolved and its lawmakers banned from politics in November after the Supreme Court ruled that it had tried to overthrow the government - something the CNRP has denied.

The CNRP dissolution was followed by the arrest of CNRP leader Kem Sokha for plotting to overthrow the government with U.S. help, an accusation both the United States and Kem Sokha have rejected.