U2 rocked Berlin on Saturday, returning to the German city where almost 20 years ago the Irish band came to reinvent themselves and make "Achtung Baby", for many fans their best album.

"Thank you for coming to our 'grosser party' (big party)," singer Bono told a crowd of 90,000 people during a two-hour set in the Olympic Stadium built by Hitler in the 1930s. "We wrote many songs here in Berlin."

U2 came in 1990 to get inspiration from a city undergoing profound change in the wake of a peaceful revolution that pulled down the Berlin Wall the previous November and brought to an end communist East Germany.

The album that they came up with, "Achtung Baby", marked a new direction both musically and visually for the group, and would go on to sell in huge numbers and receive widespread critical acclaim.

The video for the best-known song, "One", was shot in Berlin with clips of spluttering Trabants, the archetypal Eastern Bloc car that also featured, suspended over the stage, in the high-tech "Zoo TV" world tour that followed.

The current "360" tour taking in 14 European cities before heading to North America includes an enormous spaceship-like structure straddling the stage flashing out graphics and lighting effects and blasting out a wall of sound.

The Berlin concert included a mixture of classic U2 songs like "Sunday Bloody Sunday" and "Mysterious Ways" as well as new songs from their latest album "No Line On The Horizon."

With Bono a prominent anti-poverty activist, the concert also had a political edge, with a rendition of "Happy Birthday" for Nelson Mandela and a song dedicated to detained Myanmar opposition leader Aung San Suu Kyi.

"This woman has been under house arrest for the best part of 20 years," Bono said. "I would like to sing her an Irish lullaby."