The Continuity IRA has carried out a bomb attack in Co Fermanagh on the property of Lord Brookeborough, an elected unionist hereditary peer who sits on the Policing Board.
It is the first time a member of the new Policing Board has been targeted, and some of Lord Brookeborough's colleagues last night expressed concern at the development.
A caller to The Irish Times yesterday said the paramilitary group had planted a bomb on the Colebrooke estate in Brookeborough. The caller, who used a recognised code word, said the Continuity IRA would oppose anyone who attempted to legitimise the "the renamed colonial police force".
British army explosives experts were already at the estate after a loud bang had been heard.
The leader of the House of Lords, Lord Williams, told peers that an attack "with explosives" had taken place on Lord Brookeborough's property. The peer is an honorary colonel in the Territorial Army and son of former Northern Ireland prime minister, Lord Brookeborough.
He runs a farming and tourist business from his 1,000-acre home. It is understood he was not on the estate at the time of the explosion but his mother said it had been on a road outside and no-one had been injured.
A second device was not found but a security operation was continuing in the area last night. Police said it was expected to last several days. CIRA is the only republican organisation not formally on ceasefire. Co Fermanagh is one of its strongest bases and it has carried out several attacks in the area.
Meanwhile, there was a security alert at Belfast International Airport last night. Police were searching the terminal building and car parks after a bomb warning. Passengers were warned of lengthy delays.
Earlier, two masked men, one armed with a handgun, tried to board the Belfast-to-Dublin Enterprise train. The men tried to board at 9.10 a.m. as the train travelled through Kilmore, outside Lurgan, Co Armagh. A window in the driver's cab was broken during the incident. He was not hurt and continued to Belfast where he raised the alarm.
The incident happened as the train slowed in open countryside. It started when a man walked onto the track, a Translink spokesman said.
"The driver's response was to sound the horn and slow the train down. As he slowed it something hit the side window of his cab and shattered it," he added.
Police sources said they were investigating all possibilities, including paramilitary involvement. The incident was condemned by SDLP deputy leader Ms Bríd Rodgers, who said: "The Enterprise is a real example of North and South working together for mutual benefit. It is used by people from both sides of the Border and all sides of the community in the North."
The INLA has been blamed for a "punishment" attack on three men in Ardoyne in north Belfast. They were found in an alleyway between Northwick Drive and Eskdale Gardens on Tuesday night. They had each been shot in the right leg. The INLA is also thought to be responsible for a gun attack on a Protestant man in Ardoyne earlier this week. Local SDLP Assembly member, Mr Alban Maginnis, said: "Once again the INLA have shown themselves to be utterly irresponsible."
In Derry, a man in his 20s was also shot in the leg after a group of men forced their way into a house in Herne Way early yesterday. A couple and their 11-week-old daughter escaped injury after a masked man, armed with a sawn-off shotgun, entered their home in Shetland Street in Antrim.
Meanwhile, thousands are expected to attend the funeral today of Mr Gerard Lawlor (19), the Catholic man who was shot dead by the UDA in north Belfast on Monday.