US rapper Cardi B cancels a concert in Indianapolis.

US rapper Cardi B cancelled a concert in Indianapolis Tuesday evening due to concerns over a "security threat," she said on social media.

Indianapolis police confirmed the cancellation, citing an "unverified threat to the artist."

"There is no immediate threat to public safety, this (is) not an active incident. Ongoing investigation," the department said on its official Twitter account.

The 26-year-old rapper posted a video on Twitter and Instagram of what appeared to be rehearsals at the Bankers Life Fieldhouse earlier in the day.

"Dear Indiana people I'm so sorry for today," she posted on Twitter.

"Unfortunately there was a security threat that is currently under investigation right now. My safety and your safety first."

On Instagram she said, "Im so sorry guys I never dealt with a situation like this before and I'm not taking any chances.I love you guys," followed by two heart emojis.

The superstar, who has a one-year-old daughter with her husband, the rapper Offset, also posted a screenshot of a statement from the show's promoters Mammoth Live saying the concert had been postponed due to "a security threat and safety concerns."

Annoyed fans tweeted that the show was canceled only "minutes" before it was scheduled to start, but others expressed their support for "caring about our safety."

Bankers Life Fieldhouse's Twitter account said the concert would be rescheduled for September 11 and promised to honor tickets for the show's original date.

Agence France-Presse