Loyalist paramilitaries have been linked to two gun attacks in north Belfast in which a 19-year-old man was killed and another critically injured.
19-year-old was shot dead in house in Woodvale area
The dead man was shot after three men burst into a house in Dhu Varren Crescent in the Woodvale area at about 0400 BST. He died later in hospital.
The other man was shot several times as he walked two dogs on the Crumlin Road near Glenbank just before midnight.
Police are linking the attacks to tensions between the UVF and LVF.
A short time after the killing, in nearby Woodvale Pass, a man escaped another apparent murder bid by jumping out the window of a house as a number of masked men were attempting to smash their way into it.
BBC Northern Ireland security editor Brian Rowan said the UVF is believed to have carried out the murder and the LVF to be responsible for the first shooting.
Loyalist sources have said neither victim was a member of a paramilitary group.
Chief Superintendent Phil Wright said police were very concerned by "how the tensions have increased" between the rival loyalists.
"The police at the present time have deployed their resources onto the streets," Mr Wright said.
The shootings happened in north Belfast
"We would appeal for vigilance out there. We would ask people to be very wary about what's going on, who they see, about what people are doing and if they have any concerns report any of that activity to the police."
Detectives have asked for anyone who saw a light blue Peugeot 405 that may have been used by the killers to contact them.
It was found on fire in Cupar Way in the Shankill area a short time after the fatal attack.
The name of the man who was killed has not yet been released.
The shootings came just 24 hours after an attack on a home in the nearby Ballysillan district.
Earlier this month, loyalist paramilitaries were blamed for the murder of a man shot dead as he drove a lorry in east Belfast.
He was Jameson Lockhart, 25, from the Ballysillan area of north Belfast.
The DUP's North Belfast MP, Nigel Dodds, has condemned the overnight shooting incidents
He said: "These incidents would appear to be linked to the tensions between the UVF and LVF following on from the murder in east Belfast recently.
"These events are sickening and appalling. The ordinary people of north Belfast do not want this violence.
"I appeal for calm and restraint at this very difficult time. As we approach the 11th night bonfires and the Twelfth itself it is vital that everyone with any influence uses it to defuse the situation."