The attacked marred West Ham's 3-2 win over the English giants in the final match at the London club's Boleyn Ground on Tuesday night. The match was delayed for 45 minutes because of the incidents.
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"It was an extraordinary night full of extraordinary moments in front of extraordinary fans, 99 percent of whom behaved impeccably and were a credit to the club," the club said in a statement.
"However, we are aware that there were some supporters outside the Boleyn Ground who didn't act in an appropriate way when the Manchester United team bus was damaged.
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"That was not acceptable and we will work with the police to identify those responsible and ban them for life."
West Ham co-chairman David Sullivan had initially blamed United for the delay to kick-off, saying they should have arrived earlier at the ground.
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