When the global credit crunch first hit Kazakhstan in August 2007, Nursultan Nazarbayev, the president of the oil-rich country, pledged that no big bank would fail.

But the partial default by BTA last week has raised fears of a looming bankruptcy at Kazakhstan's biggest bank that would intensify pressure on the troubled financial sector - and provide a crucial test case for the scores of western banks that have extended loans or cut derivatives deals with the Kazakh group.