The Protestant leader of Northern Ireland's power-sharing government has launched a blistering attack on his Sinn Fein coalition colleagues, accusing them of attempting to intimidate the police into freeing Gerry Adams without charge.

The 65-year-old Sinn Fein leader remained in police custody for a fifth day Sunday. Adams is being questioned about allegations that he was Belfast commander of the outlawed Irish Republican Army in 1972 and ordered the abduction, killing and secret burial of a widowed mother of 10.

The senior Sinn Fein politician in the unity government, Martin McGuinness, has warned that his party's continued support for law and order could depend on Adams' treatment.

First Minister Peter Robinson on Sunday accused McGuinness of "a despicable, thuggish attempt to blackmail" police. Adams could be released Sunday night.