Celtic chief executive Peter Lawwell believes there is a social problem in Scotland and wants answers to the threats against his club.It comes after the club's manager, Neil Lennon, was attacked while on the touchline during their 3-0 win over Hearts on Wednesday and a bullet was posted to him at Celtic Park a day later.

Lawwell said there was a deep problem that needed to be addressed.

"The pressure that everybody's working under, particularly the football, is enormous," he said.

"It's just not right. It's a society problem here that somebody has got to grasp."

"We're the only football club that's subject to these vile, relentless attacks in Scotland and somebody has got to ask why. Why is it Celtic and why is it no-one else and why is it continuing?"

The rivalry between Celtic and Scottish Premier League leaders Rangers hit its fieriest during their Cup meeting on March 2.

Lennon was involved in a heated exchange with Rangers assistant boss Ally McCoist as Steven Whittaker, Madjid Bougherra and El Hadji Diouf were all sent off for Walter Smith's team.

Lawwell said threatening incidents directed at the club were becoming more common.

"Take a look at this week. Apart from last night, seven people were arrested for alleged offences at our training ground," he said.

"Today, we had police removing a package that allegedly holds ammunition, which they have taken away for forensic tests. And that's this week."

The league will go down to the wire between Celtic and Rangers with Lennon's side a point behind ahead of Sunday's last game of the season.