Two men arrested over the murder of IRA informer Denis Donaldson have been released without charge.

The suspects, aged 31 and 69, were arrested in the Republic on Tuesday evening.

A garda spokesman said investigations are ongoing.

Mr Donaldson, a former senior Sinn Fein officer from west Belfast, was shot at a remote cottage in Co Donegal on April 4, 2006.

No one has been charged over the 56-year-old's murder and the arrest is understood to be the first by gardai.

Months before his death, Mr Donaldson publicly revealed that he had been working as an informer inside the republican movement for years.

A senior officer has described the case as "complex".

The suspects - who had been held at Letterkenny garda station, Co Donegal, under Section 30 of the Offences Against the State Act - were released on Thursday night.