Permission denied (publickey).

I'm trying to clone a repository using this command:
{{{
sudo git clone git@bitbucket.org:ianwalter/slimming-stem.git
}}}

I'm getting the following error:
{{{
Cloning into slimming-stem...
Permission denied (publickey).
fatal: The remote end hung up unexpectedly
}}}

The public key under my /home/username/.ssh/id_rsa.pub
seems to be the same as the one I've added to my account settings so I'm not sure why I'm getting denied.

Thanks,
Ian