The leader of the Catholic Church in Scotland was sent bullets in the post before the papal visit last year, it was reported today.
Cardinal Keith O'Brien received the bullets at his home in Edinburgh, the Daily Record newspaper said.
He told the Record the bullets were "a horrific incitement to violence and deeply regrettable".
Police said they could not comment on the allegations, which came after it emerged that Celtic manager Neil Lennon was twice sent a parcel bomb.
Two more prominent Celtic fans, Paul McBride QC and former Labour MSP Trish Godman, were also targeted.
The club, formed in 1888 by Irish Catholics, draws its support largely, but not exclusively, from Catholics.
Police said the two packages sent to Lennon, and others to lawyer Mr McBride and Ms Godman, were "designed to cause real harm to the person who opened them".
Lennon, 39, has endured threats and abuse throughout his career and was forced to retire from representing Northern Ireland in international football after claiming he had received death threats from a paramilitary group.
He was the victim of a street attack in the west end of Glasgow in 2008 and earlier this year also received a package containing bullets.
Celtic players Niall McGinn and Paddy McCourt, both from Northern Ireland, were also sent bullets.
Mr McBride is one of Scotland's most-recognised QCs and is a well-known Celtic fan.
Last week he accused the Scottish Football Association (SFA) of bias in favour of Rangers when assistant manager Ally McCoist and players Madjid Bougherra and El-Hadji Diouf all escaped bans for misconduct during an Old Firm Scottish Cup clash at Parkhead.
Ms Godman, who has stepped down as an MSP, was deputy presiding officer of the last session of the Scottish Parliament as well as Labour MSP for West Renfrewshire.
On her final day as an MSP, she was pictured wearing a Celtic football top at Holyrood.
The Catholic Church in Scotland was unavailable for comment.
Police investigating the letter bombs said they want to speak to three people who could have "vital information" about the attacks.
A young couple and a man with a dog were seen walking near a post box in Montgomerie Terrace, Kilwinning, Ayrshire, around 2pm on Friday April 15. A Royal Mail worker intercepted a parcel bomb there which was addressed to Paul McBride QC.
Police said the post box was a "focal point" of the investigation.
The man is in his 30s, wore glasses and a baseball cap and was walking a black and brown Staffordshire bull terrier-type dog.
The young couple comprised a man wearing a black hooded top and a woman described as small and slim. They were walking with a dark-coloured Staffordshire bull terrier-type puppy, thought to be around eight weeks old.
They were described during house-to-house inquiries in the area.
Detective Chief Superintendent John Mitchell of Strathclyde Police said: "We would like these potential witnesses to come forward as they could have vital information which might help our investigation.
"Anything they may have seen or heard on the street at that time could provide us with clues which could lead us to the person or people responsible for these crimes.
"We can't stress enough that any information is of interest to us, something that may seem insignificant could actually be the piece of information we need. If you know something, get in touch.
"The person or persons who are responsible for this have not just caused massive distress and worry to the intended targets, they have also placed the people who handle the mail in harm's way.
"They must be caught and they must be brought to justice."
Police also said they believe no "general threat" has been made to Celtic fans as a whole.
Chief Superintendent Ruaraidh Nicolson said: "I would like to make it absolutely clear that the people who have received these packages appear to have been targeted for comments they have made in recent weeks.
"We do not believe that this is a general threat to all Celtic supporters or other high-profile supporters of the club.
"We are giving appropriate advice to people who we believe should be getting it.
"It is really unhelpful to have lots of media and public speculation as to who has been receiving this guidance. It only serves to create further fear and alarm in our communities."