US rapper B.o.B
US rapper B.o.B Reuters

Prominent US rapper Bobby Ray Simmons - better known as B.o.B - is at the center of an internet row following a string of bizarre tweets in which he claimed the earth is flat and denied the holocaust.

The rapper first drew mockery and criticism in (almost) equal measure, with a string of posts on his Twitter account insisting the earth is not spherical but, rather, flat.

The rapper posted dozens of tweets starting as early as Sunday offering "proof" of his theory.

Here's a tiny sample:

But when he was challenged by leading US astrophysicist Neil deGrasse Tyson, B.o.B doubled down on his statements.

Tyson branded the rapper "five centuries regressed" in his thinking, quipping:

To which B.o.B responded... by asking him if he is a Freemason:

Things then got stranger still, with the rapper posting a new song in which he accused Tyson of being paid by the government to claim that the earth is round: "Neil Tyson need to loosen up his vest / They’ll probably write that man one hell of a check."

But the track, called "Flatline", isn't limited to strange, unscientific theories about the earth being flat.

In it, B.o.B veers into other conspiracy theories, including something about "mirror aliens" - and holocaust denial, urging fans to read infamous holocaust denier and discredited historian David Irving. 

"But before you try to curve it, do your research on David Irving," he raps, before implying that US President Barack Obama is part of a Jewish conspiracy: "Stalin was way worse than Hitler / That’s why the POTUS gotta wear a kippah.”

Weird, right? But don't worry:

Well, for a moment you did have us worried...