Concerns about civilian deaths in Libya could hamper NATO's ability to carry out future operations outside the territory of its members, in North America and Europe.
Although Russia co-sponsored the U.N. resolution authorizing intervention in Libya, it later said NATO had "grossly violated" its mandate. This was a factor earlier this year when Russia opposed a U.N. resolution calling for action to stop the violence in Syria.
HRW highlighted an attack on the village of Majer, 160 km (100 miles) east of Tripoli on August 8, when NATO air strikes on two family compounds killed 34 civilians and wounded more than 30.
HRW said NATO had told it that the Majer compounds were a "staging base and military accommodation" for Gaddafi forces, but had not provided specific information to support that claim.
"During four visits to Majer, including one the day after the attack, the only possible evidence of a military presence found by Human Rights Watch was a single military-style shirt - common clothing for many Libyans - in the rubble of one of the three destroyed houses," it said.
NATO said it had now looked into each credible allegation of harm to civilians and confirmed that the targets struck "were legitimate military targets, selected in a manner consistent with the U.N. mandate".
(Reporting by Sebastian Moffett; Editing by Robin Pomeroy)