The Thai government, however, has indicated it is unlikely to let Rainsy even into Thailand on "national security" concerns. The government had expected opposition supporters to attempt to disrupt the event.
Security on Saturday was heightened.
Police with assault rifles massed at the Poipet border crossing with Thailand on Saturday, local time. The army was present in and around Phnom Penh airport, and traffic police reportedly carried AK-47s in the capital.
"Still it is a positive gesture on the part of the Hun Sen regime".
"We must understand that as the leader of the democratic voice in the region, Malaysia must lead by example in advocating that everyone's rights be respected".
The decision comes as Kem Sokha's political partner, Sam Rainsy, is waylaid in Malaysia with other CNRP officials after attempting a highly publicised comeback on 9 November, Cambodia's independence day.
Cambodia earlier this week invalidated 12 passports of opposition supporters who were overseas, including Sochua's. Malaysia and Cambodia are both members of the Association of Southeast Asian Nations, which maintains a policy of noninterference in each other's affairs.
In response to the United Nations and USA statements, CPP spokesman Sok Ey San said Friday that Cambodia's government has no intention to negotiate with Sam Rainsy, adding that troop buildups along the border between Cambodia and Thailand had been made to "maintain political stability and security for the people" during celebrations to mark Independence Day and the Water Festival. "More countries in ASEAN need to emulate Malaysia going forward if the bloc is ever going to shake the moniker of being primarily a dictator's club".
Sam Rainsy had been blocked on Thursday by Thai Airways from boarding a flight from Paris, where he lives in exile, to Bangkok. Other legal cases have since been lodged against him by the government.
More than 50 more people have been arrested in recent weeks since Rainsy said he planned to return home from self-exile in France to rally opposition to Mr Hun Sen.
"On behalf of the Cambodia National Rescue Party, I urge... the global community to increase pressure", he said.
"They (Cambodian government) had requested to us to send them back to Cambodia, if they reach our country, " he said when met by Bernama after giving a group ceramah in conjunction with the Tanjung Piai Parliamentary by-election at a house in Kampun Teluk Kerang, near here last night.
Rainsy holds dual citizenship, and according to Robertson, he entered Malaysia on his French passport. "It's unpredictable and anything can happen".
Kin Phea, the director-general of the International Relations Institute at the Royal Academy of Cambodia, said on Sunday that if Rainsy had any intention of returning, there were ways to land in the Kingdom.
The saga of Sam Rainsy's return also elicited a response by U.S. Senator Ed Markey, who tweeted on Thursday that Hun Sen had "undermined democracy and rights" in Cambodia and demanded that he allow CNRP leaders to return over the weekend, adding that he had introduced to Congress a bipartisan resolution calling for their peaceful repatriation "so he knows we're watching".
FILE - Nurul Izzah Anwar, right, daughter of imprisoned Malaysian opposition leader Anwar Ibrahim, leads a chant in Kuala Lumpur, March 17, 2015.
He only arrived, however, in Malaysia's capital, Kuala Lumpur, where he is scheduled to meet politicians on Tuesday.
"Only in Hun Sen's repressive Cambodia would letting someone out of house arrest after two years on politically fabricated charges be considered "progress" of some sort".
The Trump administration, also on Friday, condemned the recent arrests and reminded Malaysia of its obligations under global law barring the return of people to face torture.
Still, the likelihood of him making it back to Cambodia appears slim.
Amnesty International called on the Cambodian authorities to "stop pressuring neighboring governments to harass, intimidate, arrest and detain Cambodian citizens with links to the outlawed political opposition".