A brothel in Cologne was forced to black out the flags of Saudi Arabia and Iran from a huge World Cup soccer-themed advertising banner after angry Muslims complained and threatened violence.

The 24-metre-high by 8-metre-wide (78 by 26 ft) banner displayed on the side of the building features a scantily-clad woman and the slogan: "The world as a guest of female friends," a variation on the World Cup slogan: "The world as a guest of friends".

The flags of the 32 nations taking part in the month-long soccer tournament which kicks off in June are shown below.

Those of Saudi Arabia and Iran have been covered with black paint, according to a worker at the brothel who would only give his name as Peter.

"Some people turned up and demanded that we remove the flags," Peter told Reuters. "First they were sensible but then they became threatening. The management here decided to do it so that we didn't get any more trouble."

"They didn't want these two flags to be associated with this go-go girl on the banner as it's a brothel and it offended their religious feelings," said a spokeswoman for the Cologne police.

"The owner removed the flags even though he wasn't legally obliged to as no crime had been committed."