Celtic have vowed to "remain strong in the face of intimidation" after it emerged that two viable parcel bombs had been sent to manager Neil Lennon.
Paul McBride QC, who represented Lennon in his recent disciplinary dealings with the Scottish Football Association, and MSP Trish Godman, a Celtic supporter, have also been targeted, with Strathclyde Police revealing the four packages - which were all intercepted - were "designed to cause real harm to the person who opened them".
Celtic chief executive Peter Lawwell appealed to supporters to stay calm and only respond through support for Lennon, who has been the subject of tight security measures since another item, initially thought to have been a hoax, was intercepted by Royal Mail staff on March 4.
Lennon last week admitted the off-field issues, which have required him to be put under 24-hour surveillance, had put a "slight strain" on his home life but his love for his job meant he would not give up and Lawwell promised to continue providing support to the Northern Irishman.
Lawwell said: "Neil Lennon is a football manager who simply wants to carry out this role to the best of his professional ability. However, in this horrific ongoing campaign, he and other Celtic personnel continue to be the subject of repeated threats and intimidation.
"It is an intolerable state of affairs which must end. Celtic, from our inception, has been a club open to all. We enjoy friendship and respect throughout the world yet, here in Scotland, we are caught up in these vile events.
"The most recent targeting of Neil Lennon, Paul McBride and Trish Godman - three people who are linked only by an affinity with Celtic - deserves condemnation from all right-minded people."
Lawwell appealed to Celtic fans to "respond only through positive support for Neil and the team".
He added: "Celtic and its supporters are more united than ever and we thank them for their expressions of goodwill to Neil at this time. Celtic supporters should rest assured that Neil will continue to receive the full backing of everyone at the club. They should also understand that we will remain strong in the face of such intimidation."
Strathclyde Police Detective Superintendent John Mitchell said sending the packages was a "despicable and cowardly act".