Photos and video from Madrid show riot police confronting Leicester fans as blue smoke flares are set off and chants of "Gibraltar is ours" can be heard.
Dozens of riot police armed with shields and batons were seen as shirtless Foxes fans shouted and waved their arms as chaos broke out with fans claiming police attacked innocent bystanders.
Objects, inclduing glass bottles, were thrown at police and fans left injured as violence gripped the square.
Dozens of riot police armed with shields cleared a square of Foxes fans
Fans were seen with blood pouring down their faces.
A witness told BBC 5 Live: "There were a couple of people who probably antagonised the police, but then they took out all these people here.
"There were people with children, they came in with batons and there was a 70-year-old man and the kids in the way."
Another Foxes fan said: “An 18-year-old was looking for his dad, police came up and were hitting him with a baton, he was doing nothing.”
Dramatic images as Leicester City fans CLASH with police in Madrid
Wed, April 12, 2017
Photos and video from Madrid show riot police confronting Leicester fans as blue smoke flares are set off and chants can be heard.
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Thousands of Leicester fans have travelled to the Spanish city for their Champions League quarter-final first-leg game against Atletico Madrid.
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The clashes were condemned on social media with Twitter users comparing Leicester to Dortmund fans.
One Twitter user said: “Monaco-Dortmund fans showing some serious class while Leicester fans are busy fighting the cops. They call themselves classy!”
Another branded the Foxes fans “a disgrace”.
Violent clashes broke out between Leicester fans and police in Madrid
Blue smoke flares were set off in Plaza Mayor
Riot police cleared one of Madrid's main squares
Hours before kick-off at the Vicente Calderon tensions escalated in Plaza Mayor Square.
Flares and bottles were thrown as riot police used batons to clam the crowds.
It is believed a number of arrests have been made.
Last night Spanish media said police were forced to use “riot control measures” against 300 fans.
It comes as security has been stepped up in Germany following yesterday’s attack on a bus carrying the Borussia Dortmund team.
The attack forced a 24-hour postponement of the team's high-profile clash with AS Monaco.
Since when were Leicester fans hooligans? ������
— James (@JamesHarms94) April 12, 2017
Spain discovering that despite what it might have read last season, Leicester are the same as every other English club when it comes to fans
— Enough Of That (@AndyGilder) April 12, 2017
Monaco-Dortmund fans showing some serious class while leicester fans r busy fighting the cops. They call themselves classy!#ChampionsLeague
— A sane freak! (@bourne_rohieyt) April 12, 2017
leicester fans are a disgrace
— ㅤ (@griezrnann) April 12, 2017
Officials said security had been stepped up for the rescheduled match tonight, and for a second Champions League quarter-final between Bayern Munich and Real Madrid.
German Chancellor Angela Merkel, who takes a keen interest in the fortunes of Germany's national soccer team, has praised Dortmund fans for taking in AS Monaco supporters overnight so they could stay on for the postponed match.
The solidarity prevailed as the two teams entered the stadium and prepared for the quarter-final match, with fans from the two teams drinking together and hugging each other.