By Martin Plaut
Africa editor, BBC World Service
China's largest oil firm is looking to expand internationally
Human rights activists, including actress Mia Farrow and a number of Nobel Prize winners, are appealing to Swiss bank UBS to end its role in launching PetroChina on the Shanghai stock exchange.
PetroChina is controlled by the China National Petroleum Corporation, the largest operator in the Sudanese oil industry.
The letter, signed by personalities including Senator Romeo Dallaire, the former UN commander in Rwanda, and Mukesh Kapila, former UN humanitarian co-ordinator for Sudan, expresses deep concern at the role of UBS in the launch of PetroChina.
The signatories say that the Chinese National Petroleum Corporation provides revenue to the Sudanese government - helping pay for its war in Darfur. In addition, they accuse the company of benefiting from the forced displacement of locals from oil concessions.
And they say the company allows the Sudanese military to use landing strips and refuelling facilities in its oil concessions.
In reply UBS says it cannot discuss the work of its clients, but points out that although CNPC is a controlling shareholder in PetroChina they are two separate legal entities.
The bank maintains it neither deals with clients in Sudan, nor with companies that generate a significant share of their revenue from Sudan.
Nick Donovan, of the Aegis Trust, which is launching the letter, described the UBS position as no more than a legal fig leaf.
Aegis Trust is appealing to members of the public to put pressure on the bank to change its stand.