The Saudi-led coalition bombing rebels in Yemen has been using US-supplied cluster munitions in its air campaign, Human Rights Watch says.

The widely banned bombs contain dozens of submunitions, which sometimes do not explode, becoming de facto landmines that can kill or maim long after they were dropped.

Washington defended its transfers of cluster munitions, saying they were subjected to stringent requirements.

"Recipients of such transfers must commit that cluster munitions will only be used against clearly defined military targets and will not be used where civilians are known to be present or in areas normally inhabited by civilians," a US Defence Department official told AFP.

"This is obviously a critical element of the policy."

HRW said it had gathered photographs, video and other evidence indicating that cluster munitions had been used in coalition air strikes against the Huthi rebel stronghold of Saada province in Yemen's northern mountains in recent weeks.

It said that analysis of satellite imagery suggested that the weapons had landed on a cultivated plateau, within 600 metres of populated areas.

Cluster munitions are prohibited by a 2008 treaty adopted by 116 countries, but not by Saudi Arabia and its coalition partners or the United States.

"Saudi-led cluster munition air strikes have been hitting areas near villages, putting local people in danger," said HRW arms director Steve Goose.