The capability of dissident republican groups to carry out gun and bomb attacks in the Republic and in Northern Ireland is increasing, according to gardaí.

They say they have discovered sophisticated homemade explosives, timing units and firearms in a variety of searches over the past two years.

Over 30 suspected dissident republicans were arrested last year, 22 of who were brought before the Special Criminal Court on terrorist-related charges.

Assistant Garda Commissioner John O'Mahoney, who is in charge of the garda units responsible for targeting subversive and criminal organisations, said these groups continue to present a very real threat, particularly in Northern Ireland.

He said while they have very little public support, they pose a real threat to the lives of innocent people, as well as businesses, the economy, and to the peace process.

Gardaí displayed a sample of the firearms and explosives they have seized from dissident republicans over the past two years.

The display at Garda headquarters included a beer-keg bomb, homemade mortars, sniper rifles, revolvers, a Sten machine gun, AK47 assault rifles as well as timing units, Semtex explosives, detonator cords and ammunition.

These were found in searches all over the country, including in Louth, Monaghan, Wexford, Kildare, Cork and Mayo.

Sinn Féin leader Gerry Adams appealed to dissidents to stop any activities that are not peaceful.

He said he and Martin McGuinness had publically called on dissidents to meet and talk with them but this was refused.

Mr Adams said there was no popular support for what they are doing.

Fianna Fáil justice spokesperson Niall Collins has said the warning over the capacity of dissident groups to launch attacks is "extremely serious".