Theresa May: Martin McGuinness moved Republican movement towards peace in Northern Ireland
Theresa May has said Martin McGuinness moved the republican movement towards peace.
The Prime Minister recognised Mr McGuinness' work in securing a number of significant political agreements.
Mrs May said: "Martin McGuinness served the people of Northern Ireland as deputy First Minister for nearly a decade. We recognise his work over the many years securing a number of significant political agreements.
"He played a key role in moving the Republican movement towards a position of using peaceful and democratic means. I want to send him best wishes for his retirement.
"We will all continue to work to make sure the people of Northern Ireland are able to live freely and in peace."
Sinn Fein president Gerry Adams hailed him as a patriot and peacemaker as tributes flooded in from across the political spectrum.
The Sinn Fein president said they first met more than 45 years ago behind the barricades of Free Derry, a no-go zone for the British army, and had been friends and comrades since.
"I also want to thank Bernie (his wife) and the entire McGuinness family for the support they have given to Martin over many years and for allowing him to become the leader, the patriot, the peacemaker and poet that he is."
He said he had been shocked by Mr McGuinness's recent appearance.
"Thank God he is looking a lot better since then and responding well to the treatment he is receiving. However, he does need to take time out to get better for himself, for his family and for our struggle."
He added: "Martin has said he wants to come back and be part of the process to end partition, build reconciliation, unite our people and achieve Irish unity.
"Give him the space to get better and increase our efforts so that when he returns the process of change has advanced."
Northern Ireland Secretary James Brokenshire said he was sorry the former deputy first minister would not be standing for another term at the Assembly.
He said: "I thank him on behalf of the Government for his work in securing a number of significant political agreements as well as his service as deputy first minister of Northern Ireland."
Nationalist SDLP leader Colum Eastwood said Mr McGuinness had lived nearly his whole adult life in public.
"I hope he is now given the time and the opportunity in private to rest and regain his health.
"I was especially heartened to hear Martin's good spirits and his determination to overcome his recent illness."
He said it was telling that his Derry rival found his true calling in politics.
"He was the longest serving minister in our Executive and there is no doubting his commitment to the institutions that were established under the Good Friday Agreement.
"Perhaps most significantly, Martin McGuinness developed the ability to reach out beyond his own base and in recent years has acted generously to reach out the hand of friendship and reconciliation. That ability was best displayed in his relationships with Ian Paisley and Peter Robinson.
"It was a rare gift and came as much from his personality as it did from his politics. Sinn Fein will miss him."
Ulster Unionist leader Mike Nesbitt said he had been a major influence over the 10 years since the DUP decided to work with Sinn Fein in Stormont Castle.
"His decision to take up arms in the IRA and terrorise the people of Northern Ireland has left a legacy we are still struggling to come to terms with.
"That said he is clearly unwell and I wish for him and his family what I would wish for myself and mine."
Alliance Party leader Naomi Long recognised the degree to which he stretched himself and his constituency over recent years to move the political process forward.
"During that time he displayed significant moments of generosity, which were important in building relationships and securing the peace we enjoy," she said.