Saudi Arabia and the UAE are trying to shut down a UN-backed war crimes investigation in Yemen, HRW said on Friday.
The 47-member United Nations Human Rights Council in Geneva is divided into two distinct groups.
One group made up of European countries and Canada calls for a one-year extension after investigators issued a damning report saying the conflicting governments of Yemen, Saudi Arabia and the UAE could be responsible for war crimes in Yemen.
The second group, led by Arab state Tunisia on behalf of the Saudi-led coalition, makes no mention of extending the probe but calls for Yemen's almost defunct National Commission of Inquiry to continue investigating the conflict.
The two sides could bridge differences before the council session ends on September 28.
"By definition, there are differences," council spokesman Rolando Gomez said Friday. "One speaks to technical assistance. One is slightly more of a condemnatory nature. There are informal consultations that are under way. There are always efforts to meet in the middle."
Mona Sabella, an international advocacy officer at the Cairo Institute for Human Rights Studies, said independent investigations like those led by experts were important for the credibility of the council.
She said failure to renew or strengthen such mandates would "empower repressive governments that want to destroy the UN human rights system."
"The choice is clear for UN member states: Support the renewal of independent and international investigations into war crimes in Yemen, or bow to Saudi threats and allow these investigations to be quashed," she wrote in an e-mail. "Nothing would make Saudi Arabia and the UAE happier than to do away with independent investigations into war crimes in Yemen."
HRW described the Saudi attempt to kill the investigation as a "blatant attempt to avoid scrutiny."
"The Saudi-led coalition's campaign to discredit and undermine a UN investigation into abuses by all Yemen's warring parties is yet another blatant attempt to avoid scrutiny of the coalition's own actions in Yemen," John Fisher, HRW's Geneva director, said in a statement.
"The Human Rights Council cannot afford to fail Yemeni civilians. States should renew the mandate of the (probe) or risk the Council's credibility," he added.
Saudi-led forces are accused of numerous war crimes in Yemen including the bombing of civilian targets such as a school bus and hospitals.
The Saudi-led aggression on its southern neighbor Yemen has turned the impoverished Arab country into what the UN has described as “the world's worst humanitarian crisis.”
Since the Saudi-led campaign in Yemen started in March 2015, some 15,000 Yemenis have been killed and thousands more injured. Millions risk disease and starvation.