Uefa has asked local authorities to step up security for open training sessions at Euro 2012, reports BBC Sport.
The request follows the racial abuse of Dutch players by some spectators watching training in Krakow last week.
An increased police presence at training grounds is one option that Uefa have asked to be considered.
"Any such behaviour is totally incompatible with Uefa's zero-tolerance policy," a statement said.
"While to date there has only been one isolated incident, Uefa is confident the local authorities will adequately deal with the issue."
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