Host cities of Euro 2020 football matches need to better monitor the movement of spectators, including before they arrive and after they leave the stadiums, the World Health Organization (WHO) said on Thursday.

"We need to look much beyond just the stadia themselves," Catherine Smallwood, Senior Emergency Officer at WHO's European office, told a press conference when asked about recommendations in the face of rising cases in London and Saint Petersburg.

"What we know is that in a context of increasing transmission, large mass gatherings can act as amplifiers in terms of transmission," Smallwood added.

The British capital is due to host the semi-finals and final of the tournament next week, while the Russian city will host the quarter-final between Switzerland and Spain on July 3.

Also, Italy has warned any fans from England not to try to use loopholes in COVID-19 travel restrictions to sneak into the Euro quarter-final between England and Ukraine in Rome on July 3, even if they have a ticket.

In an effort to prevent the spread of the highly contagious Delta coronavirus variant, Rome last month introduced a five-day quarantine for anyone coming to Italy who had been to Britain in the previous two weeks.

It made an exception for short-stay business trips and visitors in transit, but on Thursday the Italian embassy in London issued a statement saying anyone in the country under these circumstances will not be let into the stadium.

"Being exempt from quarantine in Italy for any legal reason will not translate into permission to enter the stadium," the Italian embassy wrote. "Fans based in the UK should therefore not travel to Italy to attend the match on Saturday at the Stadio Olimpico in Rome."

Widescale checks are expected as people enter the stadium. Anyone found to have ignored general quarantine rules faces a fine of up to 3,000 euros ($3,555), the Italy's health ministry website says.

UEFA has said 16,000 fans will be let into Saturday's game - 25 percent of its total capacity.

Hundreds of cases have been detected among spectators attending Euro matches, including Scots returning from London, Finns returning from Saint Petersburg and carriers of the more contagious Delta variant in Copenhagen.

(With input from agencies)