The Bangladesh government will free opposition leader Khaleda Zia from jail on Tuesday for six months so she can get medical treatment, a minister told AFP.

Law and Justice Minister Anisul Haq said the move came after a brother and sister of Zia -- who has been in prison for two years -- appealed to Prime Minister Sheikh Hasina to let her arch-rival fly to London for treatment.

Hasina and Zia are bitter rivals whose families have dominated Bangladesh's politics since independence in 1971.

Haq said, however, the 74-year-old Zia would not be allowed to go to another country. "On the basis of the application and having been directed by the Prime Minister Sheikh Hasina, Begum Khaleda Zia's conviction has been suspended," Haq told AFP.

She is freed "on condition that she remains in her Dhaka residence to receive treatment and does not go abroad".

There was no immediate comment from Zia's family or her Bangladesh Nationalist Party (BNP). Sentenced to 10 years jail on graft charges, Zia also faces nearly three dozen other outstanding cases. The BNP says the charges are politically motivated to keep her out of politics.

Her lawyers have had repeated bail applications rejected. They have argued that she could die in prison without proper treatment. A recent leaked medical report on Zia's health said her rheumatoid arthritis was becoming increasingly serious. She has already had two knee replacement operations.

"As a result of combined active disease and accompanied damage she is, at present, at a crippled state and largely dependent on assistance for her day-to-day activities," the report said.

Hasina took over as prime minister from Zia in 2009 and has ruled since.