* UN rights boss Pillay cites executions of civilians, bombs
* Rebel courts give death penalties by stoning, decapitation
(Adds civilian casualties, paragraph 7; ICC, 11)
By Stephanie Nebehay
GENEVA, July 10 (Reuters) - The United Nations human rights chief said on Friday Islamist insurgents in Somalia had executed civilians and set off bombs in residential areas, violations which she said may amount to war crimes.
Navi Pillay, U.N. High Commissioner for Human Rights, cited credible reports that rebels had also set up tribunals which have handed down death sentences by stoning and decapitation and also ordered amputations.
Civilians, especially women and children, are bearing the brunt of the latest violence in the lawless Horn of Africa country, she said, as government troops try to drive insurgents out of their bases in the capital Mogadishu.
"Witnesses have told U.N. investigators that the so-called al Shabaab groups fighting to topple the transitional government have carried out extrajudicial executions, planted mines, bombs and other explosive devices in civilian areas and used civilians as human shields," Pillay said in a statement.
"Fighters from both sides are reported to have used torture and fired mortars indiscriminately into areas populated or frequented by civilians," she said. "Some of these acts might amount to war crimes".
Al Qaeda-linked fighters in al Shabaab control much of southern and central Somalia and all but a few blocks of the capital. Neighbouring countries and western governments fear if the Somali government is overthrown, the country will become a safe haven for al Qaeda training camps and militants will destabilise the region.
Hundreds of civilians are believed to have been killed and wounded since the offensive led by al Shabaab and Hisbul Islam militia began in May, Pillay said. Insecurity has prevented aid agencies from reaching many of the more than 200,000 people who have fled Mogadishu during the period.
The former U.N. war crimes prosecutor said rights activists, aid workers, journalists and the displaced are especially vulnerable. Six journalists have been killed in Mogadishu this year, including four apparently assassinated, she said.
There was also increasing evidence that "various forces" in Somalia are recruiting child soldiers, a serious violation of international human rights and humanitarian law, she said.
"Once order has been restored — and one day order will be restored — those responsible for human rights violations and abuses should, and I hope will, be brought to justice," said Pillay, who is from South Africa.
Her spokesman Rupert Colville, asked whether a case could be brought to the International Criminal Court (ICC) amid raging conflict, noted that the Hague-based tribunal had indicted leaders of Uganda’s Lord’s Resistance Army (LRA) and warlords from the Democratic Republic of Congo.
Regular judicial institutions have ceased to function in Mogadishu and southern and central areas, Pillay said.
"U.N. human rights staff have received credible reports that in areas controlled by insurgent groups, ad hoc tribunals are judging and sentencing civilians without due process and in violation of Somali as well as international law," she said.
"The punishment handed down by these tribunals include death sentences by stoning or decapitation, as well as amputation of limbs or other forms of corporal punishment," Pillay added.
In the Somali town of Baidoa on Friday, witnesses described how hardline Islamist rebels beheaded seven people for being "Christians" and "spies" in the latest implementation of strict sharia law by al Shabaab. (Editing by Charles Dick)