50 Cent postpones European tour

US rapper 50 Cent has "temporarily postponed" his European tour, prompting questions over whether he has retired from making music.

The star is currently poised to lose a chart battle with rival Kanye West. He vowed to quit if his album, Curtis, was outsold by West's Graduation.

West topped the UK charts on Sunday, and he is expected to win the race to number one in the US later this week.

A spokeswoman for 50 Cent refused to comment on his retirement plans.

She said that "unforeseen circumstances" had led to the temporary postponement of his tour.

The rapper was also due to perform at this week's Mobo Awards and Vodafone Live Music Awards in London, as well as an MTV show in Germany on Friday. Those appearances have also been scrapped.

Simultaneous release

West and 50 Cent, whose real name is Curtis Jackson, both released their third albums last week.

Jackson threw down the gauntlet last month in an interview with hip-hop website SOHH.com.

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

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

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

The same year, West's Late Registration sold more than 860,000 copies in seven days.

Both rappers will learn their US chart positions when the final rundown is revealed on Wednesday.