UPDATE 1-Libya said to use cluster arms, Tripoli denies it
* Rights group says use of cluster munitions "appalling"
* Libyan government rejects allegation
(Adds detail, background, changes dateline)
By Fredrik Dahl
TUNIS, April 15 (Reuters) - A U.S.-based rights group accused pro-Gaddafi forces of using cluster munitions in the Libyan rebel-held city of Misrata, endangering civilians.
A Libyan government spokesman rejected the allegation.
Cluster munitions -- fired from artillery or rockets -- can scatter bomblets over a wide area. They often fail to detonate immediately and may explode years after a conflict, killing or maiming people, according to humanitarian groups.
Human Rights Watch said in a statement that government forces had fired cluster munitions into residential areas in the western city of Misrata, "posing a grave risk to civilians".
The group said it had observed at least three such weapons explode over the coastal city's el-Shawahda neighbourhood on the night of April 14.
"Researchers inspected the remnants of a cluster submunition and interviewed witnesses to two other apparent cluster munition strikes," it said on its website, which also had photographs of what it said were the remnants of the munitions used in Misrata.
Steve Goose, Human Rights Watch arms division director, said: "It's appalling that Libya is using this weapon."
"They pose a huge risk to civilians, both during attacks because of their indiscriminate nature and afterward because of the still-dangerous unexploded duds scattered about," he said.
PROVE IT, LIBYA SAYS
Based on a submunition first discovered by a New York Times reporter and inspected by Human Rights Watch, the group said the cluster munition was a Spanish-produced MAT-120 120 mm mortar projectile, which it said opens in mid-air and releases 21 submunitions over a wide area.
It said it had not yet been able to determine if civilians in Misrata had been wounded or killed by such munitions.
A rebel spokesman in Misrata, the insurgents' last major enclave in western Libya, also told Reuters cluster munitions had been used by pro-government forces there.
Mussa Ibrahim, a government spokesman, dismissed the allegations: "I challenge them to prove it."
Referring to the presence of humanitarian groups, he said:
"To use these bombs, the evidence would remain for days and weeks, and we know the international community is coming en masse to our country soon, so we can't do this."
Libya has invited UNICEF to visit Misrata and on Saturday a Red Crescent and Red Cross team will go there, he said.
Government forces have laid siege to Misrata for more than six weeks. Hundreds of civilians are believed to have been killed, and the rebels have warned of an impending massacre unless NATO intensifies its air strikes.
Human Rights Watch said a majority of countries in the world have banned the use of cluster munitions through the Convention on Cluster Munitions, which became binding international law in 2010. Libya has not signed it, it said.
(Additional reporting by Mussab Al-Khairalla in Tripoli; editing by Michael Roddy)