World MotoGP champion Valentino Rossi has reportedly gone into hiding in Italy after being named in a letter from a terrorist organisation.

According to Italian media reports, a letter bomb was sent to the Milan offices of Iberian airlines warning the Repsol Honda rider to sever all connections with Spanish oil group Repsol-YPF.

An unnamed police source told Reuters news agency that the rider was under police protection and that security measures had been taken.

These are news items which do not concern sport Honda boss Carlo Fiorani

The communication was said to have been sent by an anarchist group believed to behind a spate of letter bombs in Spain and Italy.

Rossi is based in London but has returned home for an awards ceremony.

Rossi's team boss Carlo Fiorani told the Gazzetta dello Sport website: "We are stunned and struck by the news that we have learned from the newspapers.

"Repsol are the sponsor of Honda and not of Valentino Rossi.

"In any case these are news items which do not concern sport and we do not know the situation which could have generated this news."

Rossi completely dominated the first season of MotoGP, taking the title after winning 11 races.

The 23-year-old has won 50 of the 108 grands prix he has ridden in.