Human Rights Watch (HRW) says Saudi airstrikes on a funeral in the Yemeni capital constitute an apparent war crime, calling for an independent probe into the incident.

In one of the deadliest attacks in Yemen, Saudi warplanes bombarded a funeral hall packed with mourners in Sana’a on Saturday, killing over 140 people and injuring at least 525 others.

"The clear presence of several hundred civilians strongly suggests that the attack was unlawfully disproportionate," the leading rights group said in a statement on Thursday.

It called for an “independent international investigation of this atrocity” as Saudi Arabia “has shown its unwillingness to uphold its legal obligations to credibly investigate.”

The group said Saudi Arabia has used its position in the Human Rights Council “to obstruct efforts to establish an international inquiry into ongoing violations in Yemen.”

Therefore, the Saudi regime “has no place on the UN body," the New York-based group added.

It also said remnants of munitions found at the site of the Saturday attack showed they were American made, adding it holds Washington responsible for the role of its forces in any unlawful attack.

A failed BLU-108 canister with two submunitions still attached is seen after an attack on the quarry of the Amran Cement Factory in Yemen, on February 15, 2016. (Photo by Human Rights Watch)

"After unlawfully attacking schools, markets, hospitals, weddings and homes over the last 19 months, the Saudi-led coalition has now added a funeral to its ever-increasing list of abuses," said HRW's Sarah Leah Whitson.

The group called for both the US and UK to immediately suspend all arms sales to Saudi Arabia.

Human Rights Watch has repeatedly documented Saudi use of US- and UK-manufactured weapons, including cluster munitions, in unlawful attacks in Yemen.

The US continues to sell arms to the Riyadh regime, approving more than $20 billion in military sales in 2015 alone, despite increasing recognition that the kingdom may use the weapons unlawfully.

Three US arms sales in 2015 and 2016, worth nearly $3 billion, involved replenishing Saudi weaponry used in Yemen. Last month, US Senate endorsed a military deal with Saudi Arabia worth $1.15 billion.

The British government also continues to sell arms to Saudi Arabia, despite growing evidence of the use of UK-made weapons in Yemen.

According to the London-based Campaign Against Arms Trade, the UK has approved £2.8 billion ($4 billion) in military sales to Saudi Arabia since March 2015.