CIVIL rights campaigner the Rev Jesse Jackson has said his son had quit politics to concentrate on battling mental health problems.

Jesse Jackson Jr's resignation yesterday, just two weeks after voters re-elected him to a ninth full term in the US Congress, came months after he went on a mysterious medical leave while facing separate government investigations.

Mr Jackson Jr sent his resignation letter to House of Representatives speaker John Boehner, citing his continuing treatment for bipolar disorder and admitting "my share of mistakes".

His father told reporters his son resigned because he did not believe he could continue with his political career and try to regain his health at the same time.

"He made the decision to choose his health," he said.