Fiat's chairman 81-year-old chairman Giovanni Agnelli has revealed he is to travel to the United States for treatment "for a long-standing prostate problem".

Earlier in the week, the Italian car maker's shares surged upward on rumours - swiftly rebutted - that Mr Agnelli had died.

Investors piled into Fiat shares in the belief it would be easier for the group to sell its loss-making car manufacturer once the founder's grandson was no longer at the helm.

The shares rose again on news of Mr Agnelli's illness, but less dramatically, and soon fell back.

Mr Agnelli said he had given details about his health to halt the rumours, adding that he would retain all his responsibilities and stay in close contact with management.

Fiat is due to release its financial results for the January to March period on14 May, and to host a visit from Italy's Prime Minister Silvio Berlusconi in the same week.

The Agnelli family controls about 30% of the company's shares.

Fiat has extensive interests in the automotive, insurance and energy industries.

But Fiat's car division, which accounts for about 40% of the company's sales, racked up an operating loss of 549m euros last year.