The Continuity IRA terror unit behind a mass murder bid in Fermanagh last weekend comprises of just a dozen members.

Security sources say they know the identities of most of the renegade faction in the border county and stress it is a small group incapable of mounting a sustained terrorist campaign.

However, police chiefs warn that the CIRA remains a serious threat and is determined to kill officers in the area in sporadic attacks.

They believe that the current Continuity IRA leader is based in Co Fermanagh and that he has ordered members to escalate their activities.

A source said: “It is lucky that many of the devices they have been using have failed to explode for various reasons. The real danger is they only have to succeed once.

“Until recently they had been largely only targeting commercial centres and police stations in Fermanagh with large devices, but have switched tactics to attempt to murder police officers.

“However, we are well aware of who is behind this and there is a hardcore of around a dozen members.”

Three police officers cheated death last Saturday night when a homemade rocket failed to detonate as it was aimed at their foot patrol on Lisnaskea’s Main Street.

Two officers were treated for shock and one for minor injuries when the improvised rocket-propelled grenade failed to explode.

Just two months earlier a police patrol escaped injury when a large landmine failed to explode in the Rosslea area of Fermanagh. The same bomb gang has been blamed.

On Monday PSNI Deputy Chief Constable Paul Leighton said the presence of semtex in the Lisnaskea device was “significant”.

The Czech-made explosive was given to the Provisional IRA by Libya in the 1980s and tonnes were smuggled into Ireland.

Security sources say that disaffected Provos removed some from arms dumps as early as 1986 when the IRA and Sinn Fein split as republicans voted to end abstention from the Dáil.

Contrary to news reports, last weekend was not the first time that the dissidents have used semtex. It has been found in scores of explosive devices over the past 14 years.

The Continuity IRA used semtex for the first time in December 1994 when it planted a 1kg semtex bomb outside an Enniskillen furniture store.

In December 2000 2lb of semtex was used in a booby trap bomb planted under a car in Lisnarick, Co Fermanagh.

The Real IRA used its own stashes of semtex in bombings and traces of the high explosive were found in the remains of the Omagh bomb 10 years ago.

As the semtex is quite old experts believe it could be unstable and nearing the end of its shelf life. This may explain why the rocket failed to detonate in Lisnaskea.

The bomb gang is headed by a number of veteran republicans who were previously involved with Sinn Fein before leaving the party in protest up to 20 years ago.

These same men were behind a huge 1,200lb jeep bomb which devastated the Killyhevlin Hotel in Enniskillen in July 1996. That was the first major attack carried out by the Continuity IRA in Northern Ireland.

Based around the Newtownbutler and Rosslea areas, the CIRA unit has been the attention of heavy security force activity.

The West Fermanagh Brigade was one of the units involved in the 1987 Enniskillen Poppy Day bombing which claimed 11 lives.