WASHINGTON -- Human rights groups say Saudi-led coalition warplanes improperly used U.S.-made cluster bombs in Yemen, posing a danger to civilians two months after a cease-fire was struck in the country's civil war.
A report issued Monday by Amnesty International was the latest by nongovernmental aid groups to claim misuse of the controversial munitions, which spray hundreds of soda-can-sized bomblets over an area the size of a football field.
The reports allege that some of the bomblets -- which are designed to destroy armored vehicles, warships or other large military targets -- turned paths and fields into deadly minefields, killing at least 25 farmers, children and other civilians since early last year.
Rasha Mohamed, who led the Amnesty International investigation in Yemen, urged the U.S. government to "pressure the Saudi Arabia-led coalition to immediately provide the U.N. with exact locations of cluster munition attacks, including maps, data with the exact dates of strikes ... to reduce the potential for further civilian casualties."
Representatives from Amnesty International and Human Rights Watch said they've given photos, phone numbers and GPS coordinates of civilian casualty cases to the State Department for further investigation.
A growing international movement seeks to ban the production, use and stockpiling of cluster munitions. So far, 119 nations have joined the Convention on Cluster Munitions, which went into force in 2010, including 19 signatories.
The United States has not signed the treaty because, according to the State Department, "their elimination from U.S. stockpiles would put the lives of its soldiers and those of its coalition partners at risk."
Deliberate use of U.S.-supplied cluster munitions against civilians could put Saudi Arabia or its coalition partners in violation of U.S. end-use agreements that restrict use only to "clearly defined military targets and ... (not) where civilians are known to be present or in areas normally inhabited by civilians."
The explosives are supposed to detonate when they land. But unexploded bomblets, packed with shrapnel, can penetrate loose soil, get stuck in trees or rubble, or fall on fields where farmers later plow, posing a long-term danger.
The State Department has been investigating allegations of Saudi misuse of cluster bombs since last year, but it has yet to make any findings public. Deliberate misuse could lead to U.S. sanctions, though that is unlikely.
"U.S. officials have regularly engaged with Saudi Arabia, reminding it of its obligations under the end-use provisions and encouraging it to do its utmost to avoid civilian casualties and damage to critical infrastructure," said a State Department official, who spoke on the condition of anonymity.
The Amnesty International report said its investigators found evidence of U.S., British and Brazilian cluster bombs during their recent 10-day trip to northwest Yemen. The group said it documented 16 new civilian deaths or casualties since last summer.
A lull in fighting since a local cease-fire was agreed in March has let thousands of Yemeni civilians return home. As a result, casualties from half-buried ordnance have surged, especially near the border with Saudi Arabia.
Some members of Congress say the administration needs to determine if Saudi Arabia deliberately used the weapon against civilians.
"The public has a legitimate interest in knowing what the State Department is doing to ensure that U.S. laws are complied with," said Sen. Patrick Leahy, D-Vt. "The response from the State Department so far has been unconvincing."
Sens. Chris Murphy, D-Conn., and Rand Paul, R-Ky., have proposed a bill to limit bomb sales to Saudi Arabia to protest its conduct in Yemen. Rep. Ted Lieu, D-Calif., a former Air Force prosecutor, has proposed a similar bill in the House.
"What's going on in Yemen is a complete humanitarian disaster," Lieu said. "There has been deafening silence from the administration on the military operations there. We deserve answers on allegations of how American-made cluster bombs and other weapons are being used against innocent civilians."
Saudi Brig. Gen. Ahmed Asseri, a spokesman for the coalition, said coalition warplanes dropped cluster munitions only once, in December, and it was against a Houthi military stronghold in Saada in northwest Yemen.
"The air force is very professional; it takes all measures to conduct surgical strikes," Asseri said during a recent visit to Washington. "Each allegation, we investigate. ... A mistake can happen. ... We always regret a loss of life."
He dismissed allegations of more widespread use as propaganda.
A Saudi-led Arab coalition intervened in Yemen in March 2015 to help battle Houthi insurgents. The Shiite Muslim rebels had forced Yemen's U.S.-backed president into exile, and had seized much of the country.
The Obama administration has provided intelligence, munitions and midair refueling to the Saudi coalition, as well as advice to mitigate against civilian casualties.
The Pentagon hasn't dropped a cluster bomb since 2003, but it still sells them. In 2013, the U.S. approved a $641 million contract with Saudi Arabia to sell 1,300 CBU-105 Sensor-Fuzed Weapons, made by Textron Systems Corp., the last U.S. company to manufacture cluster munitions.
Remnants of the CBU-105 -- and the sub-munitions it carries -- were found in civilian areas, according to the Amnesty International report.
In one such case, the report said, several bomblets grabbed the attention of two brothers, ages 9 and 12, as they herded goats on April 19 near the Saudi border in northwest Yemen.
"I found the bomb and I went and gave it to my brother so he can have one and I had one," the younger brother was quoted as saying. "He hit them against each other and they exploded and I found myself lying on the ground."
His brother was killed, the report said.