A man has been found dead on a back road after a hit and run incident.
Gardai believe the 20-year-old was struck some time after being dropped off by a taxi in the Lemgare, Clontibret area of Co Monaghan at around 3am.
He was discovered by a passer-by along a minor road at about 7.30am.
Gardai sealed off the area to allow forensic investigators carry out an examination.
The state pathologist's office has been notified.
Officers are appealing for anyone with information or who saw anything to come forward.
Meanwhile a 19-year-old man was killed in a two-car crash in Co Mayo on the Headford to Ballinrobe Road outside Shrule at around 7.30am.
He was the only person in the car. The driver of the other vehicle suffered minor injuries.
The road was closed for a crash scene examination.
In Northern Ireland, 19-year-old Michael McKiver was killed in a single-car crash in Co Tyrone.
A woman travelling with him is in a serious condition in hospital after the accident on the Ballynagowan Road in Stewartstown.
The crash involving a black Vauxhall Astra was reported to police around 8am.
Cookstown SDLP councillor Deirdre Mayo, who is related to Mr McKiver, said the community had been left shocked and saddened.
"People in the Stewartstown area have been left numb at the death of young Michael," she said.
"We can only imagine the pain and suffering of the McKiver family as they come to terms with his tragic death.
"On behalf of the SDLP, I would like to offer them our most sincere sympathies.
"They are in the thoughts and prayers of the entire community as is the injured passenger who was travelling with Michael. We wish her a full and fast recovery."
A man in his mid 20s died on the N52 Mullingar to Tullamore Road South of Mullingar at about 4.40pm yesterday after a two-car crash.
© Press Association