An Irish crime gang has put a bounty of €20,000 (£17,200) on the head of a Dublin journalist, police sources say, provoking fears of another assassination similar to that of Veronica Guerin.

Irish police said on Thursday they had uncovered a plan "at an advanced stage" to have three people murdered in the city, including crime reporter Mick McCaffrey, a former reporter with the Evening Herald who now works for the Sunday World.

Six people have been arrested in connection with the murder plot. Among the others targeted is a member of the Garda Síochána and a witness willing to give evidence against the gang over an assault at a Dublin hospital two years ago.

McCaffrey has taken a number of security precautions while Gardai monitor his home and a safe house where he currently lives.

Garda sources said the gang behind the threat are from west Dublin.

Detectives believe McCaffrey has been targeted because he wrote a number of articles recently about the sexual activities of the crime gang's boss, who is currently in jail. They said the gangster became "apoplectic with rage" over the reports and ordered a hit against McCaffrey. It is understood fellow inmates read the stories and started taunting him.

McCaffrey's former Sunday World colleague, Irish Sun reporter Paul Williams, has 24-hour Garda protection following death threats from Dublin gangsters. In 2003 a crime gang with links to the Irish National Liberation Army placed a booby-trapped bomb under his car.

The threats, assaults and murder plots against Irish journalists began in 1996 when gangsters loyal to the convicted Dublin drug dealer John Gilligan shot Veronica Guerin dead as she was returning from a court case.

Her death provoked national protests and prompted the government to set up the Criminal Assets Bureau – the crime fighting unit tasked with seizing money and assets of criminals. Guerin's expose of Dublin gangland and her death was later the subject of a Holywood biopic starring Cate Blanchett.

Five years later the Loyalist Volunteer Force shot dead Sunday World reporter Martin O'Hagan in front of his wife near their home in Lurgan, Northern Ireland.

This latest threat is being taken extremely seriously by both the Garda Síochána and the Dublin media. Garda sources say the man who has taken up the €20,000 bounty from the gang is a "violent psychopath".