Two Celtic fans have been stabbed outside an Irish bar in Rome, according to reports.

Travelling supporters had been drinking inside Flann O'Brien's pub on Wednesday night ahead of this evening's Europa League second-leg clash against Lazio.

But it's thought that a group of masked thugs from the Italian side "ambushed" the supporters who were outside the pub.

BBC journalist Chris McLaughlin, who is in Rome to cover the game, shared footage on social media of police in the area shortly after midnight last night.

He wrote: "Police outside Flann O’Brien pub In Rome where two Celtic fans stabbed.

"Understood injuries not life threatening.

"Investigation underway."

READ MORE: Celtic and Lazio hit with UEFA charges after Europa League match

The Scottish Sun reports that a group of armed Lazio ultras, who had covered their faces with masks and scarves, ambushed the supporters outside the bar shortly after 11.30pm Rome time.

A witness told the paper how one fan was stabbed in the leg, adding: "They came out of nowhere. He was doing nothing wrong.

“They were shouting 'Lazio' and had masks on their faces."

Tensions had been high ahead of the match, following shocking scenes in Glasgow last week when a group of Lazio fans marched down Buchanan Street making fascist salutes.

HeraldScotland: The fans were reportedly stabbed outside the Flann O'Brien Irish pubThe fans were reportedly stabbed outside the Flann O'Brien Irish pub

READ MORE: Celtic fans warned over behaviour, banners and marches in Rome ahead of Europa League clash with Lazio

Celtic fans responded by holding up a large banner of executed Italian dictator Mussolini with the caption 'follow your leader'.

Hoops chiefs issued a fresh warning to travelling fans on Tuesday ahead of what was being described as a high-risk match.

Italian police put a 37-hour ban on the sale of alcohol surrounding the game and Celtic fans were advised to "stay in large groups",  "keep a low profile" particularly in the evening and "avoid wearing club colours".

It's thought around 9000 Hoops fans will travel to the Italian city for the match.

HeraldScotland: Lazio fans make fascist salutes in Glasgow last weekLazio fans make fascist salutes in Glasgow last week

Fans have also been advised that anyone using the supporters' shuttle service will be searched by police, with the notice warning "under no circumstances should supporters make their own way to the stadium". 

Once at the stadium, fans will be searched and asked to produce photo ID.

Bags will not be permitted in the stadium and all banners will be checked - with banners containing any political messages not allowed inside.

Celtic fans will be kept in the stadium for up to an hour after the full-time whistle before embarking on a shuttle service back to the city centre.

Celtic had issued safety advice to fans amid tensions after a match between the clubs in Glasgow last month.

Supporters are advised to avoid wearing club colours while walking around Rome, particularly in the evening, stay in large groups where possible and keep a low profile.

The club said: “There will be a prominent police presence throughout the city on the day prior to the match and on match day. Fans are advised to always follow the advice of police at all times.”

A Celtic spokesman said: “We can confirm that two fans have been injured after being stabbed last night.

“Both are now in hospital and will receive every support from the club and the British consulate in Rome.

“Again we would strongly advise supporters to closely follow all guidance issued by the club.”

The Glasgow club and Lazio were charged by Uefa over “illicit chants” heard during their Europa League match on October 24.

Celtic were also charged over the display of an “illicit banner” during the game, which they won 2-1.