AN extensive garda and FBI investigation into the alleged plot by Muslim extremists to murder a Swedish cartoonist is expected to result in more arrests in Ireland, it is understood. Gardaí have been liaising with the FBI, which will send officers to Ireland in the coming weeks to discuss progress in the case.

The exhaustive inquiry in Ireland, which involved the translation of thousands of Arabic documents as well as the trawling of the content of several seized computers, is due to be completed within four weeks. A source said "more arrests and charges" were expected. "This investigation is still very much on-going and there are possibly some serious charges coming down the line," added the source.

Two Muslim men in Ireland were charged with minor offences in March as part of the investigation into the plot to murder Swedish cartoonist Lars Vilks, whose artwork outraged many Muslims after he depicted the Prophet Mohammed's head on the body of a dog in 2007. Algerian Ali Charafe Damache (pictured) was charged with sending a menacing text message while Abdul-Salam Mansour al-Jehani, from Libya, was charged with an immigration offence after allegedly giving a false name. Damache remains in custody while al-Jehani has been released.

Acting on intelligence shared between the CIA, FBI and European security agencies, gardaí arrested seven suspects in March after raids in Waterford and Kilkenny.

A source involved in the investigation said it was now a possibility that some people in Ireland could face extradition to the US to face charges in relation to the conspiracy to murder the cartoonist.

American Colleen LaRose, who is also known as "Jihad Jane", has been charged in the US with plotting to kill the Swedish cartoonist and using the internet to enlist co-conspirators. LaRose visited Ireland last September to recruit people for a plot to kill Vilks.

Two weeks ago, two brothers in Sweden went on trial accused of fire-bombing Vilks's home. They deny the charges.