Former foreign minister Bob Carr believes the United Nations could do with a dose of Kevin Rudd's "legendary forcefulness".

There's been some speculation Mr Rudd covets the United Nations secretary general gig.

Bob Carr and Kevin Rudd in August 2013. Credit:Andrew Meares

The incumbent Ban Ki-moon finishes his second term in 2016.

Mr Carr on Saturday told reporters at a Sydney bookstore, while spruiking his memoir, that Mr Rudd had his support.