09/30/2008 at 07:20 PM EDT
postponed two concert dates this week on her nationwide Rock Witchu Tour due to an undisclosed illness, a rep for the singer said Tuesday.
Jackson, 42, has delayed her Wednesday show in Boston and a Thursday performance in Philadelphia until further notice. She will resume her tour Saturday in Greensboro, N.C.
The postponements come a day after the singer suddenly fell ill
during a sound check in Montreal and was rushed to the hospital, forcing her to cancel her Monday night show. She was released
a couple of hours later. The nature of her illness wasn't reported.
Jackson kicked off her tour promoting her latest album, Discipline
, in Vancouver on Sept. 10.