Two men were questioned by police in the North yesterday following separate traffic collisions in which a 17-year-old youth and a 29-year-old man were killed.
Meanwhile, gardaí are unlikely to release the names of two men who died in a single vehicle collision in Co Westmeath on Saturday morning until later this week, pending the results of an examination of dental records.
In the North a 17-year-old youth died after he was involved in a single vehicle collision on the Coshquin Road in Derry yesterday afternoon.
A spokesman for the Police Service of Northern Ireland (PSNI) said the incident was reported to police at about 4.10pm. One man was detained in connection with the incident and was assisting officers last night.
In an earlier incident in Co Tyrone, Gareth McNamee (29), from Ardboe near Cookstown, died when the Renault van he was driving collided with a Land Rover Discovery at approximately 1.25am yesterday.
A third vehicle, a Vauxhall Astra, was also discovered by officers near the scene of the incident, which occurred at Drum Road, outside Cookstown.
Members of the PSNI are examining the possibility that this vehicle may be connected to the fatal collision.
A man who was arrested following the incident was later released on bail pending further enquiries.
The occupants of the Land Rover are believed to have received injuries which are not life-threatening.
The PSNI is appealing for anyone who may have seen the vehicles before the collision, or who may have witnessed the incident, to contact them.
The two men who were killed in a collision in Co Westmeath during the early hours of Saturday morning were aged 19 and 32, a Garda spokesman said. The collision occurred at Greatdown, The Downs, Mullingar at approximately 1.45am.
"A car went out of control and crashed through a ditch and overturned. A fire then started in the vehicle," the Garda spokesman said.
"A passer-by managed to remove one of the occupants from the car, a 19-year-old male. He had received serious injuries, which are described as non-life threatening." All three men are from the Mullingar area.
Separately, a 28-year-old woman died in a house fire in Co Wicklow over the weekend. The fire broke out at the house in Woodlands Park, Arklow at about 2am on Saturday. The woman's name has not yet been officially released.
Gardaí are investigating the cause of the fire, but are not treating it as suspicious.
Meanwhile, gardaí in Kilkenny have released the name of a woman who was killed when she was struck by a car on Friday morning at Kilkenny Road, Freshford, Co Kilkenny. She was Kathleen Chandley (85), Prague House, Freshford, Co Kilkenny. Separately, an axle fire on the carriage of the 11.15am train from Tralee to Cork led to some disruption yesterday morning.
An Iarnród Éireann spokesman said the fire caused the cancellation of the train but no other delays. The driver of the train succeeded in extinguishing the fire. The spokesman said there was "no risk" to anybody on board and passengers continued their journey by bus.