DUBLIN (Reuters) – A dissident nationalist group in Northern Ireland will carry out armed attacks in mainland Britain as part of its campaign for a united Ireland, its representative said in a newspaper interview on Sunday.

The Real IRA, a splinter paramilitary group of the Irish Republican Army, also claimed responsibility for the 2006 murder of Denis Donaldson, a former Sinn Fein chief administrator and spy for the British, and made threats against Sinn Fein deputy first minister Martin McGuiness.

Sinn Fein is the political wing of the IRA and McGuiness was a senior IRA commander in the 1970s.

In the interview with Ireland’s Sunday Tribune the Real IRA representative said it planned to attack Britain “when it becomes opportune.”

The Real IRA, thought to a small group with only marginal support from the Catholic community, has previously shown it can carry out such threats.

In 2000 it launched an audacious missile attack on the London headquarters of Britain’s foreign espionage agency MI6. No one was hurt in the assault, but it was a propaganda coup.

The Real IRA, which has already claimed responsibility for killing two British soldiers outside Northern Ireland’s Massereene Barracks on March 7 this year, said it would also continue to target soldiers in the British province.

“Orlaigh na hEireann will continue to strike at the British occupation forces wherever and whenever we decide,” he added, using the Irish name the group refers to itself as.

The Real IRA split from the IRA in 1997 over that group’s involvement in the Northern Ireland peace process, which in 1998 ended 30 years of fighting between minority Irish Republican Catholics and pro-British protestants which killed more than 3,600 people.

The Massereene attacks were the worst since the peace deal.

The newspaper said the group will publicly admit on Sunday to killing Donaldson at a commemoration of the Easter Rising, the 1916 insurrection staged in Ireland against British rule.

Donaldson was shot dead in April 2006, four months after he admitted to being a long-serving British spy, and no group claimed responsibility for his murder.

“We always intended to claim the operation but we wanted to wait until we had first executed crown force personnel. That was secured at Massereene,” the spokesman said.

“The days of a campaign involving military operations every day or every few days, are over. We’re looking for high-profile targets, though we’ll obviously take advantage when other targets present themselves,” he said.

The newspaper said the group will also threaten McGuiness, who denounced last month’s attack as well as the killing of a policeman by another splinter group, the Continuity IRA.

“Let us remind our former comrade (McGuiness) of the nature and actions of a traitor,” read a printed version of the statement, referring to what happened to Donaldson.

“No traitor will escape justice regardless of time, rank or past actions. The republican movement has a long memory.”

The statement also threatened members of the Police Service of Northern Ireland (PSNI).

(Writing by Padraic Halpin; Editing by Matthew Jones)