Human Rights Watch says a Saudi-led coalition may have used cluster bombs in its airstrikes targeting Shiite rebels in Yemen.

In a report released Sunday, the U.S.-based group says satellite imagery indicates the munitions landed "within 600 meters of several dozen buildings in four to six village clusters."

Cluster munitions spread bomblets over a wide area, many of which do not immediately explode. The bomblets can kill or maim civilians long after a conflict ends, and have been compared to land mines.

The report says the weapons were supplied to Saudi Arabia by the United States. Saudi Arabia has denied using cluster munitions during its monthlong campaign against the rebels.

The U.N. says at least 550 civilians have been killed in the conflict, both in airstrikes and ground fighting.