Progressive Unionist Party leader David Ervine remains in a critical condition in hospital.
David Ervine became Progressive Unionist leader in 2002
Mr Ervine, 53, was taken to hospital after suffering a heart attack at his home on Sunday. He later had a stroke and a brain haemorrhage in hospital.
He was transferred from the Ulster Hospital in Dundonald to the intensive care unit at the Royal Victoria Hospital in Belfast.
Mr Ervine was a key figure in brokering the loyalist ceasefire of 1994.
He has been an assembly member for East Belfast since 1998.
A spokesman for the hospital treating him said: "He is currently in the intensive care unit of the Royal Victoria Hospital and remains critically ill."
Thoughts and prayers
Northern Ireland Secretary Peter Hain told the BBC he had "a high regard for him".
"He's brought loyalist politics a considerable distance, he's a very progressive unionist, wants to see power-sharing work and I hope he's going to be part of that."
Former Northern Ireland Secretary John Reid - the current home secretary - said his thoughts and prayers were with Mr Ervine's family at such a difficult time.
The PUP's Northern Ireland Policing Board member Dawn Purvis said on Sunday: "David took ill this morning and is being cared for in hospital. His family are with him."
Mr Ervine, who is married with two sons, became the leader of the PUP in 2002 after replacing Belfast councillor Hugh Smyth.