A military gun was used to spray police vehicles with bullets in north Belfast, a senior officer said.
Ten shots from a Kalashnikov hit two cars which were towing digital signs through a residential area near Ardoyne on Thursday night. There were no injuries.
Dissident republicans opposed to the peace process were blamed for the potentially fatal attack, the latest in a string of efforts to kill members of the security forces.
PSNI assistant chief constable Will Kerr said: “To use military-grade weapons in a built-up urban area is madness.
“They could very easily have killed other members of the public and others using the facilities in that area.
“It is time for these dissident groups to realise how futile these acts are. They won’t distract people from doing their jobs, they need to wake up to the fact that the rest of society has moved on.”
Just after 7pm on Thursday three police vehicles were driving up the Crumlin Road with rows of houses on either side. They were towing the traffic signs for use at a loyalist protest at the nearby Twaddell Avenue.
Two vehicles and one digital sign were hit by the bullets as they passed Ardoyne. Police have recovered one weapon.
Mr Kerr said: “It was very obviously an attempt to murder police officers, it showed a complete disregard by these dissident republicans for the general safety of the public. The shots were fired in the direction of Holy Cross Chapel.”
Yesterday morning 40-50 families were moved from their homes to allow police to carry out a full investigation.
The threat posed by gunmen to members of the security forces remains severe.
They have killed two police officers, two soldiers and a prison officer in recent years. Recently letter bombs have been posted to senior police commanders and Northern Ireland Secretary Theresa Villiers. A car bomb attack at a Belfast city centre car park was thwarted.