The lack of thought for the spread of COVID-19 at the UEFA Euro 2020 final was "devastating", the World Health Organization (WHO) has said.
Maria Van Kerkhove, an infectious disease epidemiologist and the WHO's Technical Lead for COVID-19, tweeted her frustration at the scenes during Sunday's match.
Around 60,000 English and Italian football supporters gathered in London's Wembley Stadium to watch the game, many not wearing facemasks or observing social distancing.
Van Kerkhove has expressed concern that the event will increase the spread of COVID-19, including the more contagious Delta variant.
"Am I supposed to be enjoying watching transmission happening in front of my eyes?" she tweeted, describing the scenes as "devastating".
"The COVID-19 pandemic is not taking a break tonight. The COVID-19 Delta variant will take advantage of unvaccinated people, in crowded settings, unmasked, screaming/shouting/singing."
The UK is currently experiencing a resurgence in coronavirus infections due to the Delta variant, detected for the first time in India.
Last month, a senior German government minister called on the British government and UEFA to cut the number of supporters allowed into Wembley.
Italy's Prime Minister Mario Draghi had also voiced concerns about the easing of restrictions in the United Kingdom.
But UK Prime Minister Boris Johnson had defended the stadium capacity allowance at Wembley, and said the matches were being hosted in a "careful and controlled manner".
Despite the concerns, Johnson is expected to confirm an end to England's social distancing rules on 19 July, while still urging caution to citizens.