Michael Jackson's summer comeback tour could be in jeopardy after promoters accused him of breaking an agreement.

The King of Pop is due to begin a 50-date residency at London's O2 Arena from July, his first gigs since 2001.

But bosses at AllGood Entertainment want to block the shows, because they say they entered an agreement with Jackson's manager, Frank Dileo last year which promised that Jackson would appear with his sister Janet Jackson and their brothers on another tour.

Jackson was allegedly banned from making another concert deal for 18 months as part of the contract, but he violated the blackout clause when he signed up for the London concert series.

According to TMZ.com, the promoters have sent a cease and desist letter to Jackson's London concert organisers.