However, speaking on a visit to a building site in the city, the prime minister said: “The council just needs to do a better job of managing the figures properly and delivering good quality services to residents.”
The Labour leader of Birmingham City Council said he was surprised when the scale of the bill was revealed.
John Cotton took over in May and said the commitment came to light when he ordered a review of the finances.
That was despite paying out about £1.1bn in claims since a landmark court case in 2012.
The claims were brought by council workers in traditionally female-dominated jobs, such as teaching assistants, cleaners and catering staff.
The GMB union, which represents thousands of council workers, said the issue had been around for a long time and that the council should have been aware.