Former US Treasury Secretary Robert Rubin is to join the world's largest financial services group, Citigroup, as a board member and chair of its executive committee.

Former US Treasury Secretary Robert Rubin is to join the world's largest financial services group, Citigroup, as a board member and chair of its executive committee.

The details of Rubin's role are still to be worked out, however joint chief executive officers Sandy Weill and John Reed say Rubin is not the designated successor to Weill and Reed.

Rubin stood down from the Treasury post in May as the longest-serving senior fig-ure in the Clinton cabinet, and has since been courted by Merrill Lynch, Goldman Sachs and Blackstone, the private equity group.

Rubin says he chose Citigroup in part because he believed Reed and Weil have a vital sense of where they want to go.