Police in Scotland called for calm yesterday insisting there was no general threat to Celtic fans ahead of Sunday's crucial Old Firm game after letter bombs were sent to the club's manager and two of its prominent supporters.
Detectives said investigations into the devices, which targeted the football boss Neil Lennon, the lawyer Paul McBride QC and the Labour MSP Trish Godman, were now focusing on a postbox at Kilwinning, Ayrshire.
They said they also wanted to talk to three people – a young couple and a man with a dog spotted near the box – in connection with the attacks, which have reopened historic tensions between Glasgow's Catholic and Protestant communities.
David Cameron, who was visiting Glasgow ahead of next month's Holyrood elections, condemned the incidents. The Prime Minister said: "It is a reminder of the appalling sectarianism that exists in some people's minds. Even as we deal with it quite effectively in Northern Ireland, it's still a problem, and it must be sought out and crushed."
Chief Superintendent Ruaraidh Nicolson called for anyone with information to come forward. "I would like to make it clear that the people who 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," he said.
Police are expected to deploy snatch squads to stamp out bigoted chanting ahead of the match, which could decide the outcome of the Scottish Premier League.