A leading Dundalk republican who is wanted in Lithuania for allegedly conspiring to acquire guns and explosives and being engaged in terrorism has never visited the country, sources close to him have said.

Under Lithuanian law, an individual can be held to have committed a crime there without entering the country, the Sunday Tribune has been told. The Vilnius authorities are seeking the extradition of Liam Campbell (46), who has previous convictions for Real IRA membership. They are claiming Campbell conspired with three others between 2006 and 2007 to obtain weapons, ammunition and explosives from the Baltic republic. His brother Michael has already spent a year in jail in Vilnius. He was part of a sting understood to have involved MI5, the garda, and Lithuanian police. He hasn't yet been charged. Lithuanian law allows a suspect to be held for 18 months, and in special circumstances longer.

Michael Campbell's family have been unable to see him since he was arrested last January, allegedly trying to buy arms and explosives for the Real IRA. He hasn't been allowed any visits or telephone calls except to his solicitor. His only contact with his family has been through letters.

Republicans have claimed it's effectively internment by remand and have picketed the Lithuanian embassy in Dublin. It is understood that Michael Campbell, who had travelled to Vilnius to buy counterfeit cigarettes, was under surveillance. It was part of a major police sting.

The Sunday Tribune has been told that, when in Lithuania, Michael Campbell was then asked if he was interested in buying weapons. He agreed, was taken to a location where guns and explosives were on display, and was arrested.

Liam Campbell, who has served two sentences in Portlaoise prison, will fight "tooth and nail" against any charges to extradite him, sources said. An extradition case is unlikely to be heard before the summer.

Campbell was detained by members of the Garda Extradition Unit at a Dundalk car park on Tuesday. When the charges in the warrant were put to him, he replied: "Write this down – I am not guilty." He is likely to be released on bail tomorrow.