Donaldson was shot dead at remote cottage near Glenties in 2006 - just months after being exposed as an MI5 operative
Two men are being questioned in connection with the murder of a British agent in Donegal more than 10 years ago.
Denis Donaldson, a former leading Sinn Féin member, was shot dead in the Doochary area of Donegal in April 2006.
It happened months after he was exposed as an agent who had worked for MI5 for over 20 years.
Two men - aged in their 30s and 40s - were arrested yesterday by gardaí investigating the murder.
They are being held at Letterkenny Garda Station.
Gardai are appealing to anyone who may have information in relation to Mr Donaldson's murder to contact Letterkenny Garda Station on 074-916-7100, the Garda Confidential Line at 1800-666-111, or any Garda station.