By Vincent Kearney
BBC NI home affairs correspondent
Dissidents have carried out several attacks on police officers recently
Dissident republicans are believed to have about 80-100 active members, the BBC has learned.
A small hardcore are experienced terrorists, previously members of the Provisional IRA.
The majority are believed to be committed to the dissident cause but lack operational experience.
There are small but relatively strong elements in Londonderry, Tyrone, Fermanagh and north Armagh.
It is estimated there could be about 250-300 others willing to lend support and some assistance, while not wanting to become active terrorists.
PSNI Chief Constable Sir Hugh Orde has said the threat from dissident republicans remains high "in certain parts of Northern Ireland".
Both the Continuity IRA and Real IRA have attempted to murder police officers in the past year, although there have been no fatal attacks.
They are believed to be attempting to recruit more experienced members, in particular former IRA bomb makers, but there is no evidence that they are being successful.
Dissidents have not been able to form a central command structure and still operate as independent, fragmented factions carrying out attacks in their own areas.
It is also widely believed that the security services on both sides of the border have a number of well placed informants amongst the dissidents.