President Michael D Higgins has led tributes to Det Garda Colm Horkan, who was shot dead in Castlerea, Co Roscommon on Wednesday night.
Det Garda Horkan, who was on duty at the time, died from fatal gunshot wounds following an incident in the town shortly before midnight.
A man has since been arrested and is being held for questioning in Castlerea Garda station.
President Higgins said the death of the garda detective has “come as a shock to us all”.
"As President of Ireland I wish to express my deepest sympathy to the family and friends of the Garda, and to all those who have been affected by this tragedy," Mr Higgins said.
"An Garda Síochána play a crucial role in our communities and this loss of life is traumatic for our society as a whole. I have contacted the Garda Commissioner to express my deepest sympathies on this terrible loss of a member of the Force."
Taoiseach Leo Varadkar has also extended his sympathies to the family and friends of Det Garda Colm Horkan.
“Every day our gardaí put themselves on the frontline of crime prevention, on behalf of all of us,” Mr Varadkar said.
“This requires regular acts of bravery and courage. Sometimes the outcome is tragic and a Garda makes the ultimate sacrifice in the course of their duties.
“Our thoughts today are with all those grieving as a result of this tragic incident.”
Minister for Justice Charlie Flanagan said he was "deeply shocked and saddened" at the shooting of a Garda member.
“His death will cause untold heartbreak to his family, loved ones and all his colleagues in An Garda Síochána across the whole country. It is also a loss to wider Irish society. His heroism and the debt of gratitude which we owe to him and his family will never be forgotten,” Mr Flanagan said.
“The women and men of An Garda Síochána serve the whole community and work to keep Ireland safe. In their everyday duty, they put the welfare of others ahead of themselves, as they work to shield us from harm and to connect our communities. It is to them that we turn in times of crisis, including during the current pandemic.”
The parish priest in Castlerea, Fr John McManus has told of the poignant scene when he performed the last rites on Det Garda Horkan.
Fr McManus had received the call just after midnight to attend at the scene which was close to the church.
“You’re never sure what the next phone call will be, when you get a call from the gardaí you never know what you face, little did I know that it was one of their own,” Fr McManus told RTÉ’s Morning Ireland.
Colleagues of the garda detective were “so professional” at the scene and it had been “so poignant,” he said. “They were literally praying with me.”
Jim Mulligan, president of the Garda Representative Association (GRA), said the garda detective who was fatally wounded was based in Ballaghaderreen, Co Roscommon, in the Castlerea District.
"A native of Co Mayo, he joined An Garda Síochána in 1995, and was an experienced detective greatly respected by colleagues. He is survived by his father, sister and four brothers," Mr Mulligan said.
“Our thoughts are with his family and colleagues at this very distressing time. Ar dheis Dé go raibh a anam.”
‘Attack on foundations of democracy’
The Policing Authority said the killing of a garda "as well as being a wilful denial of the right to life, is an attack on the essence and the foundations of our democracy".
“It is a fundamental assault on the principle of equality. In the midst of exemplary service to the community during the health emergency, the Garda Síochána will mourn the death of a colleague.”
Independent TD for Roscommon-Galway Denis Naughten said he was "absolutely shocked and saddened" to hear that a garda had died in the line of duty.
“This is devastating news for his family, the dedicated team of gardaí in Castlerea and the community,” he said. “Our thoughts & prayers are with his family at this time.”
Fine Gael TD for Sligo-Leitrim Frank Feighan expressed his horror at the shooting saying people in the town of Castlerea are "shocked and sad" this morning.
“This man was killed in the line of duty, shielding us from harm and protecting the vulnerable and it is a terrible price to pay,” he told Newstalk Breakfast.
“Our thoughts and prayers are with the family and loved ones of this garda and his brave garda colleagues and friends.”
Mr Feighan pointed out that the killing comes just short of 40 years after two gardaí were shot dead in the nearby village of Lough Glynn.
“Gardaí are of the community. They protect the community and we owe a huge debt of gratitude for their sacrifice and it is so sad that a young man is taken down in this manner.
“It is just a huge tragedy and again a huge shock in this area.”
Fianna Fail’s justice spokesman Jim O’Callaghan said “this was not just an attack on one individual; it was an attack on civilised society”.
“We need to send out the message loud and clear that we will simply not tolerate this brutal brand of criminality against members of An Garda Síochana,” Mr O’Callaghan said.
The president of the GAA, John Horan, extended his sympathies to the family of Det Garda Colm Horkan.
“The strength of the GAA is based on the strength of our volunteers and the commitment they make to serve their community, and Colm Horkan had those selfless qualities in abundance,” Mr Horan said.
“He is fondly remembered by his friends in Charlestown Sarsfields GAA club where he not only played, but where he continued to help and serve in a wide range of roles off the field.
“His commitment to others came naturally to him, and was an obvious asset in his role as a Garda.”
It is understood the shooting took place near the Garda station after the detective stopped his car and a scuffle ensued with a man, during which the man took control of the detective’s weapon and shot him.The Office of the State Pathologist has been informed and a postmortem on the garda’s remains was due to take place later on Thursday.
All the resources of a murder inquiry have already been committed to the case by An Garda Síochána.