Sinead O'Connor

As three members of Pussy Riot wait patiently for an Oct. 1 hearing regarding their appeal of a two-year sentence handed down last month, after they were found guilty on charges of  “hooliganism driven by religious hatred," Irish singer Sinead O'Connor has penned an open letter to Russian President Vladimir Putin calling for the punk band's release from prison.

Her new album has been earning some of the best reviews of her career, but Sinead O'Connor won't be staying on the road to help promote it -- citing health concerns related to her bipolar disorder, she's been forced to cancel all of her remaining tour dates for the year.