The second North American leg of the tour — tied to the release last year of her first new album since 2008 — was scheduled to begin May 14 in Las Vegas and run through August.

“Unbreakable” was released in October, and reached No. 1 on the Billboard chart, her seventh album to do so.

In December, Ms. Jackson postponed the tour, her first in four years, saying that she needed surgery and declining to comment further. (She later denied Internet rumors that she had cancer.) In March, she canceled a run of European concerts that had been rescheduled.

Writing in The New York Times, Jon Pareles said that the opening night of the “Unbreakable” tour “touched on as many hits as possible,” with Ms. Jackson playing “the woman taking charge (funk), the joyfully loyal lover (upbeat pop), the ballad singer, the woman left lonely (midtempo R&B), the party girl (dance club beats), the rocker (with guitar up front) and, in the end, the idealist.”

In a statement, Live Nation, the tour’s promoter, said that further details about the “Unbreakable World Tour” would be coming, and that fans should look for updates on JanetJackson.com and LiveNation.com.