The New York-based group said more than 160 people were killed in one month, mostly by US bombs sold to the Saudi-led coalition battling Yemen's Houthi rebels. It said the US arms were supplied after earlier violations had been publicized, and were used in airstrikes in September and October.
"The Obama administration is running out of time to completely suspend US arms sales to Saudi Arabia or be forever linked to Yemen wartime atrocities," Human Rights Watch researcher Priyanka Motaparthy said.
More than 4,000 civilians have been killed in the conflict, and some 3 million have been displaced. The fighting, along with an air and sea blockade by the coalition, has pushed the Arab world's poorest country to the brink of famine.
Rights groups have investigated dozens of airstrikes that targeted weddings, busy markets, hospitals, and schools. They have accused the coalition of committing war crimes and called for an international investigation.
Ten days later, warplanes struck a three-story house near a funeral, killing more than 28 civilians and wounding 32 in the Red Sea port city of Hodeida, the group said. "Governments selling weapons to Saudi Arabia cannot with any credibility rely on either coalition or Yemeni-led investigations to determine whether these weapons are being used against civilians," Motaparthy said. "The US, UK, and others selling weapons to Saudi Arabia should suspend these sales until unlawful attacks are curtailed and properly investigated.