The group that monitors paramilitary ceasefires is to examine the feud between the Ulster Volunteer Force (UVF) and the rival Loyalist Volunteer Force (LVF).
In a short statement, the Independent Monitoring Commission said that the killing of two men as part of the feud would be a particular focus of an inquiry "over the next few weeks".
Northern Secretary Peter Hain is considering withholding the PUP's Assembly allowance over ongoing loyalist feuding
Last week Craig McCausland (20) was shot dead at the house he shared with his partner and two children in north Belfast. His family has denied he had any link to the LVF or any other terror group.
Earlier this month, Jameson Lockhart (25) was gunned down as part of the feud as he worked on a building site in east Belfast. The attack was also blamed on the UVF.
This morning, police are investigating an attempted murder after shots were fired at a house in east Belfast. The shooting is also believed to be linked to the feud.
A man in his 30s was in the house when shots were fired at bathroom window at the back of the property on Avonorr Drive in the lower Newtownards Road area. A car was found burnt out on nearby Bendigo Street about an hour later.
The PSNI said it was looking at the possibility that the shooting was part of the feud, although they did not know the exact motive for the attack.
There have been a number of other incidents, including the shooting several times of a man walking two dogs on the Crumlin Road in north Belfast on the same night Mr McCausland was murdered.
The UVF was also blamed for a gun attack on a house in east Belfast on Monday.
The feud has once again put the links between the Progressive Unionist Party, which has one Assembly member, and the UVF and Red Hand Commando, under the spotlight.
Northern Secretary Peter Hain said yesterday he was considering withholding the PUP's Assembly allowance for another year following a report in May that indicated the UVF and Red Hand Commando remain involved in organised crime, violent and active. Mr Hain gave the PUP a week to make a case to him for the allowances to be given to them.
PUP leader David Ervine described the fine as unjust and challenged the British government to have him arrested if it believed his party had a say over what the UVF and Red Hand Commando did.
He was dismissive of the IMC. "I want to hear what are his (Peter Hain's) intelligence services telling the IMC? . . . The IMC is an annoyance, a trial by four horsemen riding Shetland ponies."
SDLP leader Mark Durkan today welcomed the IMC's decision to investigate the feud and said he had also written to Mr Hain urging him to review the UVF's ceasefire.
"People cannot be allowed to murder and maim and expect the rest of us to turn a blind eye," the Foyle MP said. "The fact is that loyalists are still responsible for most violence. They are up to their necks in attacking vulnerable communities - and poisoning their own with drugs."
The IMC was set up by the two governments last year. Its members are former Northern Ireland Assembly speaker Lord Alderdice, retired Dublin civil servant Joe Brosnan, ex-Metropolitan Police anti-terrorist squad chief John Grieve and ex-CIA deputy director Richard Kerr.
Additional reporting: PA
