At a Sean South commemoration in Limerick city last Sunday, a statement was read on behalf of Continuity IRA prisoners in Portlaoise prison, which said that Irish people who serve with the British forces are a "legitimate target" for the terrorists.
The threat was read out at the Republican Plot at Mount Saint Lawrence cemetery in front of 20 garda officers at an event organised by a faction within Republican Sinn Fein.
Last night, a MoD spokesman said they are committed to protecting all Irish members in the armed forces.
"We condemn any threat of mindless violence against members of the British armed forces," he added.
There are 400 Irish men and women serving with the British armed forces.
"The statement made by the Continuity IRA is a matter for the Garda Siochana," the spokesman added.
Gardai are continuing to investigate the incident and the home of one man who attended the event was raided in the Corbally area of Limerick on Tuesday and documents seized.
At the commemoration, a man speaking on behalf of Continuity IRA prisoners told the 60 people gathered at the cemetery: "We have seen from recent years that in this city of Limerick that Irishmen are considering a career in the British army, the same British army that holds six of our counties.
"Whether they are motivated by financial reasons or a sense of adventurism, we take this opportunity to say that the moment you don a British uniform, you become a legitimate target for the IRA."
The threat was made after nine men wearing berets, sunglasses and military fatigues marched through Limerick with a piper to the grave of Sean South.
They were observed by garda officers, but no arrests were made.
Investigating officers have since gathered recordings and photographs.
The terrorists' warning comes less than a month after it was revealed that gardai had foiled a Continuity IRA plot to murder a British soldier on a visit home to the city over Christmas.
Since last Sunday, a public spat has erupted between two factions that both claim the name 'Republican Sinn Fein'.
President of Republican Sinn Fein Des Dalton said those who took part in the commemoration were dismissed from the organisation.
However, Joe Lynch from Limerick -- who helped organise Sunday's event -- rejected Mr Dalton's claims.
"They are politically bankrupt. They are old people run by four old women from an office in Dublin,"he said.
GERRY GREGG, P14