She Tweeted that she was confronted by a "50-year-old man" after she jumped the queue while going through passport control.
She said the man had called her a "slave" and a "disgusting Nigerian".
Kelis has also said she was called "Kunta Kinte" - a black character from Alex Haley's slavery novel Roots.
The 32-year-old singer continued: "I didn't say anything at the time of the riots in London for a lot of reasons.
"It's [the UK] racially decades behind progression because everything is swept under the rug. People don't talk about it.
"People don't fight about it. Not mentioning a problem doesn't make it go away."
Officials from the Home Office say they won't be investigating the claims as they believe the abuser was a member of the public and they haven't received a complaint from her.
Best known for tracks like Milkshake and A Capella Kelis has had 10 top ten singles in the UK.
News article written by Sarah Richardson
