U.S. Rep. Michele Bachmann canceled a scheduled campaign appearance in St. Louis on Saturday for GOP Senate candidate Roy Blunt after being hospitalized with an undisclosed illness.

The 54-year-old Minnesota Republican, who is serving her second term in Congress and running for a third, apparently was admitted to a Washington-area hospital Friday with what her office described as a "sudden illness." She missed several votes on the Gulf oil spill just before the House adjourned for its August recess.

Bachmann spokesman Dave Dziok said she was in the hospital most of Friday and that doctors advised her to rest. He declined to reveal the nature of her illness. She planned to return to Minnesota Saturday, her office said.

A statement posted on Bachmann's website said she is "currently resting ... and on her way to a full and quick recovery."

The illness kept her from making a trip Saturday morning to Missouri, where she is backing Blunt, a U.S. House member running in the GOP primary for the U.S. Senate. Bachmann did address Blunt's volunteers in St. Louis via Skype.

Blunt faces Tea Party-backed state senator Chuck Purgason, who also has garnered the support of Tea Party icon "Joe the Plumber."

Bachmann's decision to back Blunt has angered some Tea Party groups in Missouri. The controversy prompted some Missouri Democrats to speculate that Bachmann might change her mind about going to St. Louis. Dziok, however, indicated that the cancellation was connected to her recovery.

Purgason's Senate bid is considered a long shot. He's raised $32,000 to Blunt's $8.2 million, according to Federal Election Commission filings.

But Samuel Wurzelbacher, known as "Joe the Plumber," is backing Purgason and has bankrolled an ad that will run in nearly every Missouri TV market, according to reports in the St. Louis Post-Dispatch.

The Democrats' leading candidate in the race is Missouri Secretary of State Robin Carnahan.

The state's primary is Tuesday.

Kevin Diaz • 703-683-5157