Northern Ireland officials investigating the 1976 IRA massacre of 10 Protestant civilians have accused the Republic of Ireland's police force of ignoring their written requests for help finding the truth.

The Irish national police, the Garda Siochana, declined to comment on Friday's testimony at a Belfast coroner's inquest into the attack near the Northern Ireland village of Kingsmill. In the 1976 attack Irish Republican Army gunmen stopped a minivan carrying a dozen textile workers, ordered the lone Catholic aboard to flee, and shot the 11 Protestants. One man survived despite being shot 18 times.

Northern Ireland's senior coroner, John Leckey, said Irish police had provided no substantive response to his requests since April to see their investigation files. Neil Rafferty, a lawyer representing the deceased, said he was shocked.