50 Cent, real name Curtis James Jackson, was Eminem's protege

"Let's raise the stakes," 50 Cent said, as the pair prepared to launch rival albums on the same day next month.

He promised if West's sales beat those of his own release, he would not produce any more solo albums.

He told hip-hop website SOHH.com that he would continue to collaborate with other artists, however.

"If Kanye West sells more records than 50 Cent on September 11, I'll no longer write music," 50 Cent said.

"I'll write music and work with my other artists, but I won't put out any more solo albums."

West is known for working with Jamie Foxx, Jay-Z and Alicia Keys

Ironically, the rapper acknowledged that he had been in the studio with West recently.

This was to try to create "a new direction for me that I couldn't get my hands on", he said.

But he added the results of their collaboration would not be heard on his forthcoming album, Curtis, because it was not the sound he was looking for at the moment.

"A lot of times they may have music planned that doesn't fit the project that you're working on," he said of the producers he recruited.

The last full-length solo album by 50 Cent, The Massacre, was the best-selling release of 2005, with 1.14 million copies bought on its first week in shops.