The SPL ruled that Celtic had taken all reasonable action to prevent such "unacceptable conduct", which was reported by police following a goalless draw against Hibernian on October 29.

The outcome of the investigation was announced days before UEFA's disciplinary body meet on Thursday to discuss accusations of "illicit chanting" during Celtic's home win over Rennes in the Europa League on November 3.

An SPL statement read: "It is not disputed that a small number of Celtic fans engaged in singing and chanting in support of the IRA. Such behaviour is unacceptable and unwelcome at SPL matches.

"It is noted that Celtic FC has condemned such activity publicly on many occasions (most recently by chief executive Peter Lawwell and by head coach Neil Lennon).

"It is important that such public condemnation should continue.

"It has been established, through the above investigation, that Celtic FC took all reasonably practicable steps before, during and after the match (in consultation and conjunction with Strathclyde Police) to minimise the likelihood of unacceptable conduct occurring and, where it did occur, to assist in the identification and prosecution of offenders.

"The ongoing work amongst the club, supporters and police to ensure that any unacceptable conduct is eradicated from Celtic Park is noted and is welcomed."

SPL secretary Iain Blair only confirmed Celtic were under investigation when questioned on the topic after the UEFA action became public.

And the lack of action is consistent with the league's stance that clubs should not be punished for the behaviour of fans if all reasonable measures had been taken to prevent it and deal with it.

But UEFA, whose probe was also sparked by police reports, have been more willing to punish clubs and national associations in similar instances.

The European governing body have fined Rangers for "discriminatory" behaviour on three occasions, the latest offences also prompting a one-match travel ban on supporters. The Ibrox club argued they had done everything possible to halt sectarian singing.

Lennon urged fans to stop pro-IRA chants in May and Lawwell made a similar plea in September after the club were "inundated" with complaints from their own supporters following a 2-0 defeat by Hearts at Tynecastle.

And Lennon said last month: "We are better than that as a club and we always have been. We just don't need it.

"We are and always have been a club open to all and we do not have issues around sectarianism.

"We have our own values and traditions but they do not include these chants. We don't want them at matches and they must stop."