A US cruise missile carrying cluster bombs was behind a December attack in Yemen that killed 55 people, most of them civilians, Amnesty International (AI) said on Monday.
The London-based rights group released photographs that it said showed the remains of a US-made Tomahawk missile and unexploded cluster bombs that were apparently used in the December 17, 2009 attack on the rural community of Al-Maajala in Yemen's southern Abyan province.
"Amnesty International is gravely concerned by evidence that cluster munitions appear to have been used in Yemen," said Mike Lewis, the group's arms control researcher.
"Cluster munitions have indiscriminate effects and unexploded bomblets threaten lives and livelihoods for years afterwards," he said.
"A military strike of this kind against alleged militants without an attempt to detain them is at the very least unlawful," said Philip Luther, deputy director of AI's Middle East and North Africa Programme.
Yemen's defence ministry had claimed responsibility for the attack without mentioning a US role, saying between 24 and 30 militants had been killed at an alleged Al-Qaeda training camp.
But a local official said 49 civilians, among them 23 children and 17 women, were killed "indiscriminately."
AI said that a Yemeni parliamentary committee reported in February that in addition to 14 alleged Al-Qaeda militants, 41 local residents, including 14 women and 21 children, were killed in the attack.
"The fact that so many of the victims were actually women and children indicates that the attack was in fact grossly irresponsible, particularly given the likely use of cluster munitions," Luther said.
AI said photographs it had obtained showed damaged remains of the BGM-109D Tomahawk land-attack cruise missile.
"This type of missile, launched from a warship or submarine, is designed to carry a payload of 166 cluster sub-munitions (bomblets) which each explode into over 200 sharp steel fragments that can cause injuries up to 150 metres (about 500 feet) away," an AI statement said.
"An incendiary material inside the bomblet also spreads fragments of burning zirconium designed to set fire to nearby flammable objects," it said.
The Yemen parliamentary committee had said when it visited the site that "all the homes and their contents were burnt and all that was left were traces of furniture," AI said.
AI said it had requested information about the attack from the Pentagon, but had not yet received a response.
Amnesty said it had obtained the photographs from its own sources, but had not released them earlier in order to ascertain their authenticity and give the United States time to respond.
In Washington, a Pentagon spokesman declined to comment on the strike, saying questions on operations against al Qaeda should be posed to the Sanaa government.
"We strongly support actions against al Qaeda in the Arabian Peninsula and cooperate closely with Yemen and other countries on counterterrorism initiatives," Pentagon spokesman Bryan Whitman said.
The United States and Yemen have not yet signed the Convention on Cluster Munitions, a treaty designed to comprehensively ban such weapons which is due to enter into force on 1 August, 2010.