Police in Northern Ireland said they suspect Irish Republican Army dissidents were behind a car bombing outside a courthouse in the city of Londonderry.
Two men in their 20s have been arrested over the attack, which caused no injuries.
Attackers hijacked a pizza delivery vehicle, loaded it with explosives and left it outside the city-centre courthouse, the Police Service of Northern Ireland said.
The device exploded as police, who had spotted the suspicious vehicle, were evacuating the area.
The force said a warning call was made to a charity in England and passed on to police minutes before the explosion.