* Justice mechanisms not established, U.N. rights chief says
* Online report intended to facilitate investigations
GENEVA, Oct 8 (Reuters) - Nepal should proceed with long-delayed plans to investigate its 10-year civil war ending in 2006 which saw abuses by both sides, U.N. High Commissioner for Human Rights Navi Pillay said on Monday.
"Perpetrators of serious violations on both sides have not been held accountable, (and) in some cases have been promoted and may now even be offered an amnesty," Pillay wrote in an introduction to an online report documenting the violations (www.nepalconflictreport.ohchr.org).
Despite the pact between the government then in power, and Maoist rebels, she said, "The transitional justice mechanisms promised in the peace accords have still not been established, and successive governments have withdrawn cases that were before the courts."
Pillay's Geneva office, the OHCHR, said the report and a linked database of some 30,000 documents detailing atrocities in the conflict, were intended to help Nepalese official bodies and non-government organisations to tackle the issue.
Together they were "designed to provide a tool...to kick-start the process of seeking truth, justice and reconciliation for the crimes committed at that time," a news release said.
Pillay, separately, said the combined "Nepal Conflict Report" and the "Transitional Justice Reference Archive" were intended as "a helpful contribution to the pressing task of ensuring justice for serious violations committed during the conflict".
The report, based on information gathered by an OHCHR team in Nepal since 2006, says at least 13,000 out of a population of 30 million died in the decade of fighting with at least 1,300 still missing, apparently victims of enforced disappearances.
But it noted the government is now citing a total of 17,000 dead.
The conflict was marked, the report said, by "unlawful killings, disappearances, torture, arbitrary arrests and rape" committed by the then-royal armed forces and the fighters of the insurgent Communist Party of Nepal (Maoist).
Nepal's Maoist-led government - involved in political squabbling with its partners and opposition parties - late last year told the OHCHR to close down its office in the capital, Katmandu, and others in regional centres.
Aides to Pillay said squabbling, and the need to balance interests, may lie behind the recent appointments of former royalist officers to senior positions in the army and police whom the OHCHR has linked to wartime rights abuses. (Reporting by Robert Evans; Editing by Michael Roddy)