A Saudi-led coalition battling Shia rebels and their allies in Yemen used a U.S.-supplied bomb in an airstrike last month on a market that killed at least 119 people, a human rights group said Thursday, further highlighting American involvement in the conflict.

The March 15 bombing targeting the northwestern town of Mastaba marked the second-deadliest airstrike conducted by the Saudi-helmed campaign since it began its war in March 2015. Condemned by the United Nations, the strike also wounded at least 47 people and left charred bodies lying next to flour sacks and twisted metal.

Human Rights Watch said its investigators travelled to the town in Yemen's Hajja province, controlled by the Shia rebels known as Houthis, and found fragments of a GBU-31 satellite-guided bomb. The group said the bomb, as well as its guidance equipment, was supplied by the U.S., matching an earlier report by British television channel ITV.

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A boy sits at the site of an airstrike at a residential area near Sanaa Airport on March 26, 2015. Another coalition bombing in Yemen, targeting the northwestern town of Mastaba on March 15, killed 119 people and may have involved a U.S.-supplied bomb. (Khaled Abdullah/Reuters)

"One of the deadliest strikes against civilians in Yemen's year-long war involved U.S.-supplied weapons, illustrating tragically why countries should stop selling arms to Saudi Arabia," Priyanka Motaparthy, emergencies researcher at Human Rights Watch, said in a statement. "The U.S. and other coalition allies should send a clear message to Saudi Arabia that they want no part in unlawful killings of civilians."

U.S. Secretary of State John Kerry, who was in Bahrain on Thursday, told reporters he does not know what weapons were used in the deadly attack, but wants all the shooting to stop.

Saudi officials said they were investigating the strike, though they previously insisted most of the casualties were Houthi combatants.

The U.S. has backed the Saudi-led campaign in Yemen, where suspected American drones continue to target alleged members of al-Qaida in the Arabian Peninsula. In November, the U.S. approved a $1.29-billion rearming program for Saudi Arabia, including thousands of similar bombs.

Canada-supplied Saudi arms

According to a CBC News analysis, Saudi Arabia is Canada's second largest weapons customer after the U.S. Over the past decade, Canada has shipped more than $28 million worth of Canadian-made guns and rifles to Saudi Arabia.

A $15-billion deal to sell light-armoured vehicles to the kingdom, signed under the previous Conservative government, has become increasingly controversial as the Middle Eastern country intensifies its involvement in a civil war in Yemen.

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Medics attend to people, injured in an airstrike on a marketplace in Yemen's northwestern province of Saada on March 27, 2015. News that a U.S. bomb was used in a deadly strike last month has intensified scrutiny over North America's role in the conflict. (Naiyf Rahma/Reuters)

Scrutiny over Saudi arms deals intensified earlier this year, when it was revealed that a Winnipeg-made LRT-3 sniper rifle sold to the Saudis for self-defence ended up in the hands of Houthi fighters in Yemen's civil war.

The air campaign waged by the Saudi-led coalition in Yemen has been increasingly criticized by human rights activists over civilian deaths. Airstrikes account for 60 per cent of the 3,200 civilians killed in the conflict, according to the UN, which has criticized coalition strikes that have hit markets, clinics and hospitals.

The war in Yemen has killed over 6,000 people in total and left more than 80 per cent of Yemenis in dire need of food, water and other aid as a result of the conflict in the Arab world's poorest country, the UN has said.

With files from Reuters and CBC News