Human Rights Watch has urged the US Congress to block the sale of aerial bombs to Saudi Arabia, warning their likely use in Yemen risked more civilian deaths.

The kingdom has led a bombing campaign in its southern neighbour since March, carrying out hundreds of strikes against Iran-backed rebels who had overran much of the country.

Despite widespread criticism of the high civilian death toll, Washington this week approved a $1.29 billion deal for more than 19,000 smart bombs to replenish the Saudi air force's arsenal. Congress has 30 days to block the sale.

"The US government is well aware of the Saudi-led coalition's indiscriminate air attacks that have killed hundreds of civilians in Yemen since March," Human Rights Watch said on Wednesday.

"Providing the Saudis with more bombs under these circumstances is a recipe for greater civilian deaths, for which the US will be partially responsible," HRW's deputy director for the Middle East and North Africa, Joe Stork, said.

"The US Congress has played a role in opposing sales of US weapons used in violation of the laws of war and should do so in this case."

HRW said last month that it had documented more than two dozen air strikes by the Saudi-led coalition that appeared to be in violation of the laws of war.

The United Nations says more than 5,700 people have been killed in the conflict in Yemen since the Saudi-led military intervention began. Nearly half of them have been civilians.