Updated

A human rights group has urged Singapore to lift a travel ban on a prominent opposition leader so he can attend a conference in Norway.

The New York-based Human Rights Foundation called on Prime Minister Lee Hsien Loong in a letter Tuesday to allow Singapore Democratic Party Secretary-General Chee Soon Juan to speak at the Oslo Freedom Forum in May.

Chee has been banned from traveling outside Singapore since he declared bankruptcy in 2006 when a court ordered him to pay heavy fines for defaming former prime ministers Lee Kuan Yew and Goh Chok Tong.

The government's bankruptcy office said in a letter earlier this month that it denied Chee permission to travel to the conference because he has failed to make a contribution to his bankruptcy estate.