STOCKHOLM (Reuters) -Shares of Finland's Neste fell 14% on Wednesday after the refiner warned that its comparable sales margin for renewable products will be weaker this year than previously forecast.

The biofuels producer and oil refiner said in a statement late on Tuesday it now sees the margin at $480-$650 per ton, down from a previous guidance of $600-$800 per ton.

The rest of the guidance for the Renewable Products unit as well as the guidance for its Oil Products division remained unchanged.

"Renewable Products' sales price outlook is affected by a decrease in the diesel market price and a continued decrease in U.S. bioticket and renewable credit prices during the second quarter, while waste and residue feedstock prices have remained stable," it said.

J.P. Morgan on Wednesday cut its recommendation on the Neste stock to underweight from overweight and reduced its share price target to 20 euros from 35 euros.

Neste's share price fell 14% by 0710 GMT to 19.07 euros.

(Reporting by Anna Ringstrom and Terje SolsvikEditing by David Goodman, Essi Lehto and Stine Jacobsen)