Reading have asked police to investigate a series of death threats made to Republic of Ireland's Stephen Hunt and Ibrahima Sonko in the aftermath of the club's recent Premiership match with Chelsea.

Thames Valley Police are analysing around 20 letters - described as "seriously threatening" by a force spokesman - which were sent to the players at Reading's Berkshire training complex, apparently by Chelsea supporters.

Although both players were subject to the hate mail, it is Hunt who was the principle target. The 25-year-old appears to be paying the price for his collision with Petr Cech, the Chelsea goalkeeper on October 14th.

Hunt struck Cech with his knee as he stretched for a loose ball, fracturing his skull. Hunt was not sanctioned by Mike Riley, the referee, but his actions infuriated Jose Mourinho, the Chelsea manager, who claimed he had deliberately set out to hurt the Czech international.

The Portuguese demanded retrospective sanctions against the Laois-born winger, although he refused to criticise Sonko, whose challenge on Cech's replacement, Carlo Cudicini, resulted in the Italian swallowing his tongue and losing consciousness.

The threatening messages began arriving at Reading's training base shortly after the match, with one claiming: "We are going to kill you for what you did to our 'keepers." A Chelsea spokesman insisted there was "nothing to suggest the threats came from Chelsea fans", although he admitted the club would be happy to help police with inquiries if evidence was found which suggested otherwise.

Steve Coppell, the Reading manager, was anxious to play down the severity of the threats last night but he admitted the threatening tone of the letters gave him no option but to ask for an immediate investigation.

"It was obviously the work of a nut but sometimes nuts can be dangerous, so that is why we got the police involved," he said.

"I don't think it will affect the players. We had one of the letters on the notice board in the dressingroom for a week or so, just to show how stupid and futile something like this is. Threats like these are not unique to these lads and I've experienced things like this myself. Football is the new religion in many ways, so there will always be extremists who take things too far."

This is not the first time Chelsea have found themselves mired in such serious controversy. In March 2005, Mourinho's claim that Frank Rijkaard, the Barcelona manager, had been in cahoots with the referee Anders Frisk during the Londoners' Champions League defeat at the Nou Camp led to the Swiss official being issued with death threats.

Frisk was eventually forced to retire while Mourinho was labelled an "enemy of football" by Volker Roth, the chairman of Uefa's refereeing committee. The Portuguese was handed a two-game touchline ban and fined £9,000 for his comments.

Mourinho's outspoken attack on Hunt appears to have had similarly serious repercussions now, although Graham Murty, the Reading captain, refused to blame him for the hate mail.

"It's impossible to say whether it would have happened without all the talk that followed the game.

"As a squad we will get around both lads and make sure we're there for them if that's what they want. I know Stephen has a very strong support structure with his family and friends and he will come through this."