NATO must account for the killing of dozens of civilians during its 2011 air campaign which helped topple Moamer Kadhafi, Human Rights Watch said on Monday.

In a report, the New York-based watchdog said NATO air strikes had killed 72 civilians, including 20 women and 24 children, in what may constitute unlawful attacks on non-military targets.

"Investigations are needed to explain why 72 civilians died," said Fred Abrahams, special adviser at Human Rights Watch.

"Attacks are allowed only on military targets, and serious questions remain in some incidents about what exactly NATO forces were striking," added Abrahams, the main author of the report.

The findings are based on visits to eight bombing sites during and after the 2011 conflict. There was "no clear military target" in seven of those sites, according to the report.

HRW urged NATO to promptly investigate these incidents and present its findings to the UN Security Council.

NATO attacks, which played a key role in helping rebels to bring down Kadhafi, left a deep rift in the Security Council.

Russia, China, South Africa and India all say NATO's tactics breached UN resolutions, while the United States, Britain, France and Germany insist their actions were legal and life-saving.

The rights watchdog acknowledged that the coalition took important steps to minimise collateral damage and that the number of casualties was "low given the extent of the bombing" in the seven-month campaign.

Another rights group, Amnesty International, said in March that it had documented 55 cases of named civilians, including 16 children and 14 women, killed by NATO strikes in Libya.