Irish police today arrested seven suspects over an alleged plot to kill a Swedish artist who drew the Prophet Muhammad with the body of a dog.

The target of the alleged assassination was Lars Vilks, who had a $100,000 (£67,000) bounty put on his head by al-Qaida in 2007, with a 50% bonus if Vilks was "slaughtered like a lamb" by having his throat cut. Another $50,000 was said to have been put on the life of Ulf Johansson, editor-in-chief of Nerikes Allehanda, the local newspaper that printed the cartoon.

The four men and three women, who were detained at about 10am this morning, are in their mid-20s to late-40s and are being held at stations in Waterford, Tramore, Dungarvan and Thomastown. Garda sources have confirmed that some of those arrested hold Irish citizenship and a number are from the Middle East. Some of those questioned have been confirmed as converts to Islam.

The suspects are being held under Ireland's Criminal Justice Act 2007. Under Irish law they can be held in custody for up to seven days.

Ireland's anti-terrorist special detective unit was involved in the operation. A spokesman for the force said: "Throughout the investigation Garda Síochána has been working closely with law enforcement agencies in the United States and in a number of European countries." The CIA and the FBI were involved in the investigation.

Vilks' cartoon caused outrage because dogs are considered unclean by conservative Muslims, and Islamic law generally opposes any depiction of the prophet for fear it could lead to idolatry.

The controversy over cartoons depicting Muhammad began in 2005, when the Danish daily Jyllands-Posten printed 12 caricatures of the prophet after a children's author said he could not find an illustrator for his book on the life of Muhammad.

The drawings sparked violent protests across the Muslim world, culminating with the burning of the Danish embassy in Damascus and its consulate in Beirut in February 2006.