An Irishman on trial on charges of procuring arms in Lithuania for militants in his homeland faced a key British intelligence witness in a closed hearing Tuesday, judicial sources said.

Officials told AFP that the Vilnius court trying Michael Campbell, 36, heard evidence from Robert Michael Jardine, described as former Irish Republican Army member who, working with Britain's MI5, posed as an arms dealer.

Campbell was arrested in January 2008 in Vilnius while meeting an undercover Lithuanian agent who also posed as a dealer. Lithuanian officers involved in the sting have already given evidence in the trial, which began in August.

Campbell faces up to 20 years in prison in the Baltic state for attempting to smuggle weapons, illegally possessing firearms, and seeking to aid a terrorist organisation.

Security-sensitive parts of the trial are being held behind closed doors.

Liam Campbell is also wanted by Lithuania

At a public hearing two weeks ago, Campbell rejected the charges. His defence lawyers claim he was set up.

Campbell is the brother of Liam Campbell, 46, one of four leaders of a dissident group, the Real IRA. They were found liable this year for an August 1998 bombing in the Northern Irish town of Omagh which killed 29 people.

Liam Campbell is also wanted by Lithuania and has been detained in Northern Ireland on an extradition warrant.

Prosecutors claim the Campbell brothers and Seamus McGreevy and Brendan McGuigan -- both of whose extradition Lithuania has requested from Ireland -- hatched the arms plot between November 2006 and January 2007.

In March or April 2007 they purportedly struck a deal with Jardine to procure arms in Lithuania. The ruse would have seemed credible, because experts note that real Eastern European traffickers have long supplied the West's militants and gangsters.