Can't erase Linux ext2 fs on my Mac

[Hagablog]

I have on a USB external a Linux partition in ext2; now I obviously can't erase it from within Linux so I want to do it on my Mac. My ultimate goal is to have a single partition. Disk Utility used to be able to repartition over the ext2 but now won't, saying

Disk Erase failed with the error:

Operation timed out

This happens when creating the partition map. I think I've narrowed the problem down to the Linux partition which when I try to erase says

Disk Erase failed with the error:

Could not unmount disk.

I find this a bit funny because the disk isn't mounted because OS X can't read ext2 (I couldn't get ext2fs to work), see my puzzle?

Thank you in advance