Referee Eddie Wolstenholme referred in his match report to missiles being thrown towards Palace players during the quarter-final clash. And having already studied video evidence of two objects being thrown from an area reserved for Blades fans, club officials have begun their own inquiry.

'We know the incidents did take place and we are carrying out our own investigation,' said football executive Terry Robinson. 'The proximity leads us to believe that it was our supporters who were involved and that one of the objects was a lighter thrown from the crowd.

'We have looked at the video and have identified that two objects were thrown onto the pitch. That end of the ground is carefully monitored anyway and should the culprits be identified the club will take the necessary action.

'We have not received any communication yet from the Football Association, but we will move on from here as and when we do.'

Earlier this season violence erupted at the end of the Yorkshire derby with Rotherham and fans invaded the pitch to taunt Leeds supporters following the Blades' shock 2-1 Worthington Cup win at Bramall Lane last month.

United were fined £2,000 and warned as to their fans' future conduct.

The FA confirmed they had contacted the club following these latest incidents.

'We have written to Sheffield United asking them for their observations on the incident,' said a spokesman.