A grenade was thrown at a police Land Rover in west Belfast in what has been described as an attempt to kill officers.
The attack happened at Milltown Row off the Falls Road at 2am.
Chief Superintendent Jonathan Roberts said a police vehicle was on a routine patrol when it was struck by an object before a loud bang was heard.
No injuries have been reported.
Chief Roberts said the incident was “undoubtedly an attempt to kill or injure police officers”.