The Saudi-led coalition carrying out airstrikes in Yemen has probably used cluster bombs, which are banned by over 100 countries, the international monitoring group Human Rights Watch (HRW) said on Sunday.

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.

Cluster bombs indiscriminately scatter smaller submunitions — often called bombies or bomblets — across a wide area, and can remain buried, unexploded, decades after a bombing campaign ends. Even over 40 years after the U.S. dropped cluster bombs on Vietnam, Laos and Cambodia, the submunitions still kill and maim civilians. The nonprofit Handicap International says that 98 percent of cluster bomb victims are civilians and 27 percent children, who often confuse the metallic objects with toys.

Most cluster bombs 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.

"Credible evidence indicates that the Saudi-led coalition used banned cluster munitions supplied by the United States in airstrikes against Houthi forces," Human Rights Watch (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 on Saturday to seek an end to the airstrikes which they described as blatant aggression against the country.

The airstrikes and fighting between the Houthis and forces loyal to President Abed Rabbo Mansour Hadi, now based in Riyadh, has worsened Yemen's humanitarian crisis, prompting aid agencies to also call for a halt to the bombing.

The HRW cited a video which the Houthis uploaded to YouTube on April 17 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 April 17 of the aftermath of airstrikes near Saada showing the remnants of two U.S.-made CBU-105 Fuzed Weapons and an empty BLU-108 delivery cannister. The CBU-105 is one of the munitions specifically forbidden by the cluster bomb ban treaty, HRW said.

Fighting around Yemen has killed more than 1,000 people, including an estimated 551 civilians since the bombings started on March 26, the United Nations said on April 24. Its children's agency UNICEF said at least 115 children were among the dead.

Al Jazeera and Reuters