DHAKA (AFP) - Bangladeshi authorities said Wednesday they planned to charge the sons of former prime minister Khaleda Zia over a ferry accident that killed at least 80 people. Shipping Minister Shahjahan Khan said the government-owned Bangladesh Shopping Corporation had filed a case against Tareque Rahman and Arafat Rahman Coco as owners of a vessel that capsized on Friday night. Their mother, Zia, is the leader of the main opposition party and both of her sons are abroad receiving medical treatment. They are being sued for the accident. We filed a case on November 30. The boat was owned by Rahman Shippers Bangladesh Limited. A case will be heard soon in the Marine Court in Dhaka, he said. Formal charges would follow. Meanwhile, rescuers in southern Bangladesh retrieved six more bodies from the ferry on Wednesday, bringing to 80 the death toll following the accident. Local police chief Zakir Hossain said three people remained missing and operations would continue until all passengers onboard the MV Coco-4 were accounted for. The triple-decker ferry was at least four times over its 500-passenger capacity when it began taking in water as it came into dock late Friday on the river Tentulia. Boat and ferry accidents due to lax safety standards and overloading are common in Bangladesh, which is criss-crossed by 230 rivers. Fridays accident came as commuters rushed to their village homes from cities to celebrate the Muslim festival of Eid al-Azha. It is estimated that more than 3,000 people have lost their lives in such accidents since 1977.