CELTIC have launched an investigation into reports of violent disorder by fans as well as complaints about the police response following clashes before the Parkhead side's Champions League match against Ajax in Amsterdam.

Six fans are due in court today while another 12 travelling supporters were released by Dutch police after paying fines of up to €500 (£420) each.

The development came after 44 people, including 28 Scots, were arrested. Dutch police said eight officers had been hurt and one knocked unconscious in the violence in Amsterdam city centre before kick-off on Wednesday.

Police said fans armed with bottles and sticks attacked plain-clothed officers in an incident described as "coming out of nowhere". Officials said the majority of those arrested were Celtic fans.

Some Celtic fans reported there had been intimidation and the club last night said it had received numerous complaints from supporters in relation to their treatment in Amsterdam. The Parkhead club said it would be launching a full inquiry into those allegations.

Celtic's statement said: "There is no question that Celtic supporters have been subjected to a high degree of provocation. Last week, our supporters were the target of missiles being thrown from Ajax supporters at Celtic Park, a night where 300 seats were damaged within the stadium.

"This was followed up by an organised attack on a group of Celtic supporters in Amsterdam on Tuesday, the night before the match. We have also received numerous individual reports of other attacks on our fans.

"The Celtic travelling support has a magnificent reputation across Europe and our fans have visited major European cities over many years without incident. Once again the overwhelming majority of our supporters behaved impeccably."

It added: "We will be liaising with the local authorities in Amsterdam, our own police and the British Consulate in order to fully understand events. We would stress that there is no excuse for any form of violent conduct."

One local TV station carried an interview with a Celtic supporter who sustained injuries to his face. He said: "Police came right through the middle hitting everybody and anybody."

Before kick-off, a large banner bearing an offensive anti-Catholic slogan was produced behind one goal. Some fans have called on Uefa to take action as part of measures to eradicate religious discrimination from the game.

A Dutch police spokesman said: "At the end of the afternoon a large group of Celtic supporters attacked police officers in plain clothes. A few of them had broken noses and needed stitches above their eyebrows and on their lips."

Celtic lost the match 1-0 and now face an uphill battle to reach the knock-out stages of the competition.

A spokeswoman for Police ­Scotland said: "We have been working closely with Dutch police and authorities in relation to security at this fixture. We have been made aware of some disorder in ­Amsterdam, with a number of Celtic fans having been arrested.

"We will continue to work with our Dutch colleagues to identify anyone responsible for carrying out acts of disorder."

Eberhard van der Laan, mayor of Amsterdam, said: "I think it is unacceptable that a group of people sees this as an opportunity to behave badly, especially if this aggression is directed towards policemen who put a lot of effort in keeping the peace."