CELTIC fans in Valencia for a European match were warned not to display Catalan flags after reports of police attacks with batons, riot shields and rubber bullets.

People as young as 15 were allegedly hurt before the club’s Europa League game against the Spanish club last night. Witnesses on Wednesday night said they did not see any signs of provocation.

Several fans shared images on social media of bruises they said were sustained from batons and guns with rubber bullets.

Supporters’ organisation, the Celtic Trust, advised fans online: “Do not take Catalan flags to the stadium.”

Mike Thom, a Scot who lives in Barcelona, relayed local reports that police became violent after seeing Celtic fans holding the estelada, the unofficial flag of Catalonia, and yellow ribbons, symbols of solidarity with jailed independence leaders.

“It seems Catalan esteladas in the hands of Celtic fans angered the police,” he told The National.

“Advice for tonight from the supporters association is not to even think of going near the Mestalla [Valencia’s stadium] with an estalada or yellow ribbon.”

Fans were also urged by the Celtic Trust to arrive at the stadium early amid warnings police were showing “low tolerance”.

Sky News reported police in Valencia, the Jefatura Superior de Policia, told them six Celtic fans have been arrested following altercations, five detained for disorderly conduct and one for alleged drug trafficking.

Valencia said in a statement yesterday that they had closed their ticket office due to safety concerns.

Davy Macnamara, from Fife, was with his 15 and 21-year-old sons at St Patrick’s Bar in the city, the youngest of whom he said was struck with a baton as they ran from police.

He said his son heard of a friend’s sister who was “beaten black and blue” with truncheons.

“It was terrifying to be involved in, it’s just horrible to be here as a dad stuck in an apartment, scared to go out in the streets in case it kicks off again,” the 47-year-old said. “I had never seen one in my life and it’s horrifying to be faced with that.”

He added fans were “filled with joy” in the bar and “didn’t see one bit of trouble” but outside riot police were waiting for them with some fans in handcuffs.

Police ushered them up one street to a crossroads where there were more Celtic fans running from police, he said.

“We stood in the street with our hands up and they charged us, and as we ran my 15-year-old son was struck in the back with a baton.”

Scott Tobin, a 26-year-old from Glasgow who was at the same bar, said he saw an elderly man being beaten with a baton and heard a 15-year-old girl was taken to hospital.

“It was quite scary, they were chasing us down the street with their riot gear on,” said. “We didn’t know what would happen if they caught us.

“Their presence was expected as deterrents if anything did happen but it seemed as if they were looking for trouble themselves.”