France (AFP) - Lyon president Jean-Michel Aulas has expressed fear over next week's trip to Istanbul after the first leg of Thursday's Europa League quarter-final against Besiktas was scarred by violence and a pitch invasion.
Police reported the arrest of a dozen Lyon and Besiktas fans with five police officers and two supporters suffering minor injuries after fighting broke out at Lyon's Parc OL.
The start of the high-risk tie in France had to be delayed 45 minutes as officials attempted to clear the pitch of Lyon fans.
Many of them had already run a gauntlet of violence outside the ground, where police used tear gas to quell outbreaks of fighting and vandalism.
According to an AFP reporter, Lyon supporters poured onto the pitch as they attempted to protect themselves from firecrackers and other objects raining down from the stands above.
"Twelve arrests from both sets of fans were made," a Lyon police spokesman said. "Thrown objects slightly injured two fans who were taken to hospital," a local authority spokesperson added.
Authorities had categorised the match as maximum risk with 1,000 stewards drafted in for the clash held in an area of France's third-largest city which is home to many people of Armenian origin.
Up to 20,000 Turkish fans, the majority living in France or Germany, were intermingled among the 35,000 Lyon supporters, on top of the 3,000 fans from Istanbul situated in the visitors' stand.
Lyon president Aulas called for calm inside the stadium via a loudspeaker.
When tensions finally subsided, the match went ahead with Lyon winning 2-1.
Afterwards, the Lyon boss told French television station W9 of his unease over next week's second leg in Istanbul.
"I hope Uefa will take all the necessary measures," he said. "It seems difficult to travel to Besiktas. When you see how this fury spilled over on all sides, we are very afraid."
Thursday's disturbing scenes rounded off a black week for European club football after the Borussia Dortmund team bus was attacked with explosives on Tuesday, just before their Champions League game at home to Monaco.
In the aftermath of that incident, which pushed the game back by 24 hours, Uefa had demanded a re-evaluation of the security measures "wherever necessary".
Turkish pro-government media were blaming French fans for Thursday night's trouble.
"The Lyon hooligans attacked children," said the Yeni Safal daily newspaper, with a picture it said showed a French fan waving a crutch in the direction of a child.
Sabah, another pro-government daily website, claimed: "Lyon hooligans attacked the Turkish fans, including women and children and afterwards, the Besiktas fans responded."
Turkish president Recep Tayyip Erdogan, who faces a referendum on Sunday which could expand his powers, told NetTV: "If the French (fans) went onto the pitch, then that's very dangerous."
But Aulas countered, arguing that his side's supporters were forced into taking dramatic action for their own safety.
"With the intense fireworks, severe injuries and homemade bombs exploding around them our fans had only one option, to take refuge on the pitch," he suggested.
"I've heard some people ask 'but how could a pitch be invaded?' Well thankfully, if they hadn't invaded the pitch, they would have been trapped by Turkish fans who had turned up in strength, some without tickets."
On next week's scheduled second leg, he added: "I don't know what needs to be done, play behind closed doors or elsewhere, but it will be too dangerous for us to play this match with the same fans that were here tonight."