The Saudi-led coalition carrying out air strikes in Yemen has probably used cluster bombs which are banned by most countries, international monitoring group Human Rights Watch (HRW) has said.
The coalition includes eight other Arab states and is receiving logistical support from the United States, Britain and France.
It has been bombing Yemen's Houthi militia and allied army units for a month in an effort to restore the government.
"Credible evidence indicates that the Saudi-led coalition used banned cluster munitions supplied by the United States in air strikes against Houthi forces," HRW said in a statement.
It said it had not been able to obtain information on possible casualties from the attacks.
Saudi Arabia's coalition spokesman was not immediately available to comment on the report.
The Houthis called on the United Nations yesterday to seek an end to the air strikes, which they described as blatant aggression against the country.
The air strikes and fighting between the Houthis and forces loyal to President Abd-Rabbu Mansour Hadi has worsened Yemen's humanitarian crisis.
The HRW cited a video, which the Houthis uploaded to YouTube on 17 April, showing objects dropped by parachute which exploded in mid air and its own analysis of satellite imagery to establish the location of the blasts in al-Shaaf in Saada governorate.
HRW also said an activist in Sanaa had provided photographs he had taken on 17 April of the aftermath of air strikes near Saada, showing the remnants of two US-made CBU-105 Fuzed Weapons and an empty BLU-108 delivery cannister.
Fighting around Yemen has killed more than 1,000 people, including an estimated 551 civilians since the bombings started on 26 March, the United Nations said on 24 April.
Its children's agency, UNICEF, said at least 115 children were among the dead.
Most cluster bombs, which contain groups of smaller bombs that explode over a wide area, were banned by 116 countries in a 2008 treaty.
However, the signatories did not include any states in the Saudi-led coalition or Yemen or the United States.
The CBU-105 is one of the munitions banned in that treaty, HRW said.