Uefa has confirmed that nine of the 12 host cities for this summer's Euro 2020 will have spectators attending games.
Host associations were asked to submit plans to accept fans by 7 April before the deadline was extended to 19 April.
On 13 April, Italy said Rome's Olympic Stadium would allow 25% capacity.
The three remaining cities - Munich, Bilbao and Dublin - have five days to provide additional information on their plans before final decisions are made whether they can host matches.
The tournament, delayed a year because of the coronavirus pandemic, will take place between 11 June and 11 July.
London, Glasgow, Dublin, Amsterdam, Copenhagen, St Petersburg, Bilbao, Munich, Budapest, Baku, Rome and Bucharest are all due to host matches.
Budapest is aiming to host spectators at full capacity, while Baku and St Petersburg have confirmed a 50% capacity, although the Russian city is hoping to increase that figure.
Hungary, Azerbaijan and Russia are the only nations that are planning exemptions from entry restrictions and requirements. Ticket holders travelling to these countries may be able to avoid entry bans or quarantine requirements.
Amsterdam, Bucharest, Copenhagen and Glasgow have confirmed a minimum capacity of between 25%-33%, although that figure could yet rise for the venues in the Netherlands, Romania and Denmark.
The Football Association expects 25% of Wembley to be used for its three group matches and one last-16 game, and is hoping to have more fans for both semi-finals and the final.
"Uefa wishes to express its appreciation to its member associations and the national and local authorities who are collaborating closely in ensuring the safe return of spectators to the stadium," said a Uefa statement.
Here, BBC Sport looks at each country's preparations.
Wembley, with a capacity of 90,000, is set to host the final on 11 July among its seven games - along with both semi-finals, one last-16 game, and all three of England's group games.
The British government has said up to 10,000 spectators will be permitted inside English grounds from mid-May, and unlimited numbers from 21 June.
However, BBC Sport understands the English FA has told Uefa it hopes Wembley will be able to host about 20,000 fans for the group games (the number allowed for the FA Cup final in May), and many more for the knockout matches.
The FA has said it is prepared to host any additional games that cannot take place elsewhere, having already picked up extra matches originally allocated to Brussels.
There were concerns that a failure to confirm fan numbers might result in Glasgow being removed as a host city, although First Minister Nicola Sturgeon said last month she remained hopeful Hampden Park would stage Euro 2020 matches this summer.
On Wednesday, the Scottish government gave approval for 12,000 supporters to attend games at Hampden in June.
That is 25% of Glasgow's 51,000-capacity stadium, where three group games - including Scotland's Group D fixtures against the Czech Republic and Croatia - and one last-16 game will be played.
Dublin, Republic of Ireland
There are growing fears that Dublin may not be able to host Euro 2020 games, after the Football Association of Ireland (FAI) told Uefa it cannot provide assurances on minimum spectator numbers.
The FAI, acting on Covid-19 guidance from the Irish government, said "the matter will be kept under review", although it previously admitted it would only remain a host venue if it could guarantee fans would be permitted at games.
Dublin's Aviva Stadium is due to stage four games - three group games and one last-16 tie.
At least 12,000 spectators will be able to attend matches in Amsterdam, The Royal Netherlands Football Association (KNVB) has confirmed.
The Johan Cruyff Arena, which can hold 54,000 fans, will stage three group games and one last-16 game.
"Depending on developments surrounding the Covid-19 pandemic in June, there is a chance that more fans will be allowed inside the stadium," the KNVB said.
Denmark will allow "at least 11,000 to 12,000" fans to attend Euro 2020 matches at Copenhagen's 38,000-capacity Parken Stadium, which is set to stage three group games and one last-16 game.
The Danish culture ministry said: "We will look at whether there can be even more spectators in the Parken if health conditions allow.
"It may be necessary to close to spectators if there is a spread of infection, so it will be unjustifiable from a health point of view to allow spectators to the matches."
St Petersburg, Russia
Russia expects to allow fans to attend the four games it is hosting at the 68,000-capacity Krestovsky Stadium in St Petersburg, which will host a quarter-final in addition to three group games.
The Russian committee's director Alexei Sorokin said he believed matches could be played "with the minimum of possible restrictions".
"We already have an agreement to fill the stands to 50% capacity," Sorokin said. "We are working to welcome foreign supporters and this has not been rejected by the authorities."
The authorities are considering exemption from travel restrictions for the general public and participating team supporters holding valid tickets, subject to presenting proof of a recent negative Covid-19 test result.
Bilbao had initially said it was ready to stage Euro 2020 games at the San Mames stadium at 25% capacity (about 13,000 supporters), as long as coronavirus rates dropped to levels accepted by the regional health authorities.
However, the Spanish football federation said in a statement on Wednesday that the Basque government's conditions were "impossible to meet" in time for the start of tournament on 11 June and it would therefore be unable to hold matches with spectators.
Germany are yet to give an indication of the number of fans that could be permitted, following a rise in coronavirus case numbers in the country.
The Allianz Arena, home to German champions Bayern Munich, has a capacity of 70,000 and is due to host three group games and a quarter-final.
Budapest's 68,000-seat Puskas Arena welcomed 15,180 fans for Bayern Munich's Uefa Super Cup victory over Sevilla in September.
Hungary is set to host three group games and one last-16 game and could have a full stadium, subject to spectators fulfilling strict stadium entry requirements.
"We want, if the epidemiological situation allows, as many fans as possible to watch the matches in the Puskas Arena, with maximum compliance with safety and epidemiological regulations," a Hungarian FA spokesman said.
Non-resident ticket holders traveling to Budapest will be required to present proof of negative results from two Covid-19 tests performed in the five days preceding entry into Hungary or a valid certificate of previous Covid-19 infection within six months prior to entry into the country.
Azerbaijan's football association (AFFA) will allow the country's Olympic Stadium in Baku, which can hold 69,000 fans, to be filled to 50% capacity for its three group games and one quarter-final.
While the Azerbaijan Grand Prix from 4-6 June will be held behind closed doors, supporters from overseas will be allowed to attend Euro 2020 matches in the country if requirements for a visa and Covid-19 mitigation are met.
Wales will play two of their Group A matches, against Switzerland and Turkey, in Baku.
Ticket-holding fans from a country playing in the matches may enter the country if they present proof of a recent negative Covid-19 test result.
The tournament is due to begin in Rome on 11 June, with Italy facing Turkey at the Olympic Stadium.
The Italian Football Federation (FIGC) says the country's government will allow a minimum 25% capacity at the 68,000-capacity Olympic Stadium in Rome, which will host three group games and one quarter-final.
"Italy and Rome are on board. The government approval of the public's presence at Rome's Euro 2020 matches is wonderful news that we will immediately pass on to Uefa," said FIGC president Gabriele Gravina.
"The message that the government sends to the country is one of great confidence and extraordinary vision.
"Italy is showing courage that it is fighting against the pandemic and at the same time working to restart safely according to a clear and defined programme and schedule."
The Romanian Government plans to welcome 13,000 spectators at the National Arena in Bucharest.
Set to stage a senior men's major international tournament for the first time, Romania's 54,000-capacity stadium is to host three group games and one last-16 game.
Minister for sport Eduard Novak said: "We have the historical chance to be part of a large sporting event and to demonstrate that we can honour our obligations to the highest standards of organisation and health safety."
Ticket holders may benefit from the exemption from quarantine if they present a recent Covid-19 test and limit their stay to less than three days.
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