Three defense lawyers in Germany's biggest neo-Nazi murder trial have asked the court in Munich to relieve them of their duties.

The lawyers were appointed by the court to defend Beate Zschaepe, who has been on trial since May 2012 for alleged involvement in 10 murders.

Tuesday's motion comes a day before Zschaepe is due to testify for the first time about her role in a group calling itself National Socialist Underground. The NSU's two other core members died in an apparent murder-suicide in 2011.

Zschaepe's fourth attorney, Mathias Grasel, says he will read out a statement on his client's behalf Wednesday. Her other lawyers had counseled her not to testify.

The high-profile trial has exposed numerous failings in the authorities' handling of their decade-long investigation into the murder spree.