In its report published on Monday, the US-based HRW said it had examined in detail evidence of claims of civilian deaths from eight separate Nato strikes.
In one instance, it said a first bomb killed 14 people and a second, moments later, killed 18 more who had rushed to help victims.
"We're calling for prompt, credible and thorough investigations," HRW's Fred Abrahams, the main author of the report, told BBC News.
Mr Abrahams says Nato refuses to acknowledge the deaths and has offered no compensation to families.
"Until now, Nato has taken a position of denial," he said.
"I think it will lead to unnecessary civilian deaths in the future if Nato refuses to look at what went wrong and make corrections."
In March, another human rights organisation, Amnesty International, said it had documented 55 cases of named civilians, including 16 children and 14 women, killed in air strikes.
It said Nato had failed to investigate these cases thoroughly.