Cheers for U2's free concert in front of Berlin's Brandenburg Gate on Thursday have turned to jeers after organizers erected a barrier that blocked the view of the stage from the street.

The Irish rockers delivered its mini-concert on Thursday, playing a 30-minute set of just six songs — one of which was slated for broadcast as part of the MTV European Music Awards.

Both events are taking place in the German city as part of the celebrations marking 20 years since the fall of the Berlin Wall.

The concert, which included a duet of Bob Marley's Get Up, Stand Up with surprise guest Jay-Z, was blocked from public view by a nearly two-metre-high metal barrier.

It took place on a plaza just in front of the famous gate and surrounded on three sides by buildings. Organizers closed off the fourth side with a tarp-draped metal fence so that only the 10,000 who had snapped up free tickets could see the show.

The German city is teeming with visitors amid the anniversary celebrations, with German Chancellor Angela Merkel set to host a raft of world figures — including France's Nicolas Sarkozy, Russia's Dmitry Medvedev and U.S. Secretary of State Hillary Clinton — next week.

Music network MTV, which organized the U2 concert, said it had worked with a local promoter, the city and police to install the temporary fence "to ensure the safety and security of the attendees at the event as well as residents and businesses in the area."

Fans were not pleased.

"It's completely ridiculous that they are blocking the view [for the concert]," said Louis-Pierre Boily, a 23-year-old from Quebec City who travelled to Berlin for the Berlin Wall anniversary.

"I thought it's a free show, but MTV probably wants people to watch it on TV to get their ratings up," said Boily, one of myriad tourists and Berliners who have complained about the irony of erecting a barricade around a free concert meant to celebrate the anniversary, just metres from where the original wall stood.

"It would be nice if as many Berliners as possible could take part," city-state parliamentarian Frank Henkel told the Berliner Morgenpost newspaper prior to the show.

"It would be great if the organizers would avoid barriers of any kind."

With files from The Associated Press