LONDON (Reuters) - Britain has released former Sri Lankan Tamil Tiger rebel Karuna Amman from prison where he was detained on immigration charges, it said on Friday, believing he could not be convicted of war crimes.
Amnesty International and Human Rights Watch expressed disappointment, saying police should continue to investigate the former eastern rebel commander. They accuse him of abuses including torture and child soldier recruitment both before and after his 2004 split from the mainstream rebels.
The British High Commission in Colombo and Home Office (interior ministry) in London said Karuna, whose real name is V. Muralitharan, remained in immigration detention in Britain.
Rights groups say Karuna could be deported to Sri Lanka, apply for asylum in Britain or simply linger for months or perhaps longer in detention while his fate is decided.
But Britain says he is unlikely to face charges despite a range of allegations from rights groups.
"We are deeply concerned that Karuna and his faction had allegedly been responsible for murder and abductions and are still believed to be involved in intimidation and child recruitment," the British High Commission in Colombo said in a statement.
"The Crown Prosecution Service has advised the Metropolitan Police Service that there is insufficient evidence to provide a realistic prospect for conviction of any criminal offences in the UK."
He was arrested in November in London and pleaded guilty to carrying a passport in a false name and was sentenced to nine months in prison -- which rights groups hoped would encourage witnesses on other charges to come forward.
After his split, he continued to mount hit and run attacks on his former comrades, founding a new faction known as the TMVP which was widely seen as government-backed.
The attacks on the rebels were seen as a factor in reigniting Sri Lanka's two decade-old civil war, which has now killed some 70,000 people since 1983.
His group was blamed for abductions and killings in a brutal shadow war with the mainstream Tigers, and UNICEF accused them of abducting children, including from camps of survivors from the 2004 tsunami, as troops stood by.
Karuna was ousted from the leadership of the TMVP last year, prompting his flight from Sri Lanka. The group went on to win local elections in the island's east this year.
Britain has expressed its concern as to how he acquired a genuine Sri Lankan passport in a false name -- although Sri Lanka denies issuing any fraudulent documents.
Amnesty said British police should make it clear that any witnesses will be offered proper protection as they would likely otherwise fear reprisals, while Human Rights Watch said it hoped new witnesses would come forward before he left the country.
"Should he return to Sri Lanka, the government there will still be obliged to prosecute him for alleged crimes, such as child abduction and murder -- they have no excuse not to do so," said Human Rights Watch legal and policy director Jim Ross.
The case is not seen as being linked to the arrest earlier this month of four men on terrorism charges in Britain. They were charged with conspiring to receive electronic equipment for the Tigers.
(Editing by Dominic Evans)

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