Police on both sides of the border are searching for an armed gang following the killing of a man in County Louth and the injuring of two others.
Garda believe all the attacks are linked
The attacks, which involved the use of machetes, took place during a series of car thefts on Tuesday.
The hijackers rammed a car at St Brigid's shrine at Upper Faughart outside Dundalk shortly after 2300 GMT.
It is understood a row followed during which the 37-year-old passenger was killed and the driver, 41, injured.
Gardai believe the assaults are linked to two earlier attacks.
During one, a man was wounded with a machete. He was admitted to hospital where he received 45 stitches to his arm.
In another attack, a gang stole a car from a woman motorist who had been travelling with her son.
Detectives believe the attacks may also be linked to a hijacking about an later of a white Escort van from Bessbrook in County Armagh.