Ian Paisley, a firebrand Protestant who forged an unlikely alliance with Northern Ireland's main Catholic party under a power-sharing peace deal, has been admitted to hospital, his party said on Monday.

Paisley's Democratic Unionist Party declined to comment on a report by Northern Ireland television station UTV that the 85-year-old was in intensive care.

Paisley's wife Eileen requests that the family privacy be respected at this difficult time, the party said in a statement. The precise nature of his illness was not disclosed.

As the leading light of hardline unionism, which wants to maintain links to the United Kingdom, Paisley bitterly opposed any concession to the mainly Catholic nationalist community's desire for closer ties with the Irish Republic to the south.

Paisley refused to sit in talks involving Sinn Fein, the political ally of the Irish Republican Army (IRA), which led to the Good Friday agreement that provided for a power-sharing government between the province's main Protestant and Catholic communities.

He consistently opposed Good Friday agreement as a sell-out of Northern Irish Protestants' British heritage, and his mantra of no surrender to the IRA appeared to make him ill-suited to run the province when he became first minister in 2007.

But in office, he forged a unlikely friendship with Deputy First Minister Martin McGuinness, a senior Sinn Fein figure and a former member of the armed nationalist group the IRA, earning the pair the nickname the chuckle brothers.

Paisley retired from politics in 2010 and preached his final sermon at his local church in January.

(Reporting by Ian Graham; Editing by Conor Humphries and Ben Harding)