Ireland's justice minister has warned that the Real IRA and Continuity IRA now pose a threat as serious as any paramilitary organisation did during the Troubles.

Dermot Ahern has also revealed that there is now "cross-fertilisation" between the dissident republican terror groups.

The minister said last Monday's 250lb car bomb attack outside Newry court house demonstrated a new level of sophistication.

"There seems to be cross-fertilisation; it may be more to do with acquaintances or family membership than ideology. But nonetheless it is a more worrying trend because clearly their capability is growing," Ahern said.

The minister admitted that the Real IRA and Continuity IRA both have "significant pockets" of membership in the republic. However, the terrorist attacks witnessed in the north in recent months appeared to have been organised there.

"The threat here I believe on this island is as dangerous as it was at any time during the Troubles," said Ahern.

The authorities faced a "conundrum" in responding firmly to the growing threat in a way that would not alienate some sections of the nationalist community in the north. "What they are really at is to try and bring back troops on to the streets of Northern Ireland and to destabilise the efforts of political parties in the north to bring final peace."

The attack on Monday night in Newry was the first dissident explosion since the BBC in London was attacked in 2001 and the first anywhere in Northern Ireland since Omagh in 1998. A suspected mortar was fired at a PSNI station in Craigavon on Saturday night. Last week 31-year-old Kieran Doherty was found shot dead just outside Derry. The Real IRA claimed responsibility for his murder.