Multiple skirmishes broke out between riot police and Morocco supporters amid chaotic scenes before their team’s shock penalty shootout victory against Spain.

Security forces, who also deployed mounted officers and dogs, dragged away at least three people in the most serious trouble of the World Cup. One policeman fell off his horse in the disturbances.

Organisers later blamed the trouble on hundreds of ticketless fans, who they said had tried to force their way into Al Rayyan’s Education City stadium. However others who were caught in the melee insisted they had legitimate tickets – and feared they could have got seriously hurt.

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In one clip on social media a woman wearing Spanish colours but speaking with an English accent warned police there was a baby in the crowd. “They’re going to get trampled, there’s too many people,” she said.

Other footage showed police in riot gear pushing and shoving fans – crushing them up against a fence – as well as fights breaking out.

Morocco will play Portugal in the quarter-finals – and could play England in the semi-finals next week if both teams get through.

Sources close to the organisers told the Guardian that they had deployed extra security measures – which included soft ticket checks and a far larger police presence – because they had expected Morocco fans without tickets to try to get in.

Long before kick-off, multiple checkpoints were set up outside the metro station, with fans asked to show their tickets at each stage. With 20 minutes remaining, however, police blocked the main entrance amid fears that fans without tickets were trying to barge through.

Some people showed their phones and what appeared to be their passports but were turned away. It was unclear how many people outside the stadium had tickets and how many did not.

The atmosphere outside the stadium did eventually calm down with groups of fans watching the game on mobile phones after shuffling away from the perimeter gate. Despite a large number of empty seats before kick‑off it was later announced as a sell-out with a full capacity of 44,667.

Related: A beautiful day for Bono and Morocco in last-16 shootout win over Spain

This is not the first time there has been issues involving Morocco’s fans at this World Cup. There was also pushing before the team’s last group match against Canada, with some fans also trying to climb a fence.

A statement from Qatari organisers said: “A number of unticketed supporters gathered outside the Education City Stadium ahead of the Morocco v Spain match in an attempt to gain access to the stadium. ‘Soft’ ticket checks had been established some distance from the stadium perimeter to prevent groups crowding stadium access points.

Despite this, a small group of fans were able to approach the stadium fence and were quickly dispersed by tournament security forces on the ground, with no injuries or further issues reported.

“Fans were redirected to the local free fan zone where the match was being aired. Ensuring the safety and security of every fan is of paramount importance and all decisions taken are directed towards this aim.”