Two men and a woman have died in separate road crashes in counties Limerick, Monaghan and Tipperary.
A woman in her 30s was killed in a collision involving a lorry and a car on the N2 at Mullaghnee, Annalitten near Castleblayney at around 8am.
The woman, who was travelling alone in the car, was pronounced dead at the scene and her body was removed to Our Lady of Lourdes Hospital, Drogheda.
A man in his 50s has been arrested and is being held at a garda station in the northwest.
The road has been closed and local diversions are in place.
Gardaí are appealing to any witnesses, particularly any road users who have camera footage and who were travelling on the N2 between Castleblayney and Broomfield between 7.30am and 8.15am to contact Castleblayney Garda Station on 047 77200, the Garda Confidential Line on 1800 666 111, or any garda station.
In Co Limerick, a man in his 20s was killed and four other people were injured in a collision involving two cars, on the N21 at Ballymurragh West at around 12.50am.
The man, who was driving one of the cars, was pronounced dead at the scene. His body has been removed to University Hospital Limerick, where a post-mortem examination will be carried out.
Two teenage girls and a man in his late teens were seriously injured in the collision, while another man in his 20s was taken to University Hospital Kerry with non-life threatening injuries.
All four were travelling in the second car.
The road has been closed and local diversions are in place.
Gardaí are appealing for any witnesses to contact Newcastle West Garda Station on 069 206 50, the Garda Confidential Line on 1800 666 111, or any garda station.
Separately, a man in his 20s died following a road crash in Co Tipperary last night.
The single-car crash occurred on the N24 at Cordangan Cross near Tipperary town at around 9.45pm.
The man, who was travelling alone, was pronounced dead at the scene.
His body was removed to Waterford University Hospital, where a post-mortem examination will be carried out.
The road has been closed for a technical examination and local diversions are in place.
Gardaí are appealing for any information on the movements of a 2005-registered grey Toyota Yaris in the area around Tipperary town and the Bansha Road between 9pm and 10pm.
They are also appealing to any road users with camera footage (including dash-cam) from the area to contact Tipperary Garda Station on 062 80670, the Garda Confidential Line on 1800 666 111, or any garda station.
The deaths bring to 183 the number of people who have died on Irish roads so far this year.
Three people died in two separate crashes in Co Tipperary at the weekend.
Two men, aged 18 and 20, were pronounced dead at the scene of a collision involving four cars, which occurred at Ballinunty, near Thurles on Saturday evening.
A man in his 30s died in a two-car collision on the N24 Frank Drohan Road, outside Clonmel, in the early hours of Sunday morning.
