A group of West Ham United fans were attacked and one was taken to hospital with slight injuries on Wednesday ahead of Thursday's Europa League semifinal second leg against Eintracht Frankfurt, German police said.

Police said in a statement that two vans stopped outside a pub where West Ham fans had gathered in the early hours of Wednesday.

RELATED | West Ham identifies fans who allegedly hit German reporters

A group of 15-20 people, who witnesses said were Eintracht supporters based on their face coverings, got out of the vans, entered the pub and attacked the group of British fans, injuring one of them slightly, police added.

They then got back into the vehicles and left the scene. Police said they were unable to locate the vans, with one of them having a local number plate.

"The injured guest, a 34-year-old man from Britain, was taken to hospital for medical treatment," Frankfurt police said in a statement.

Tensions are high ahead of the return leg after Eintracht won the first leg in England 2-1, with both teams bidding to reach their first European final in more than 40 years.

German reporters Philipp Hofmeister and Tim Brockmeier, who work for regional broadcaster Hessischer Rundfunk , said they were attacked by West Ham supporters during the first leg.