(In second graf, makes clear stake size mentioned by one source.)
RIO DE JANEIRO, Dec 5 (Reuters) - Brazil's Vale SA said Friday it was in negotiations with an investor over the sale of a stake in its Mozambique coal assets, responding to reports it is selling the stake to Japanese trader Mitsui & Co.
On Thursday, Reuters cited two sources as saying Vale was poised to sell a stake in its Moatize coal project in Mozambique to Mitsui. One source said a 15 percent stake would be sold to Mitsui for about $450 million.
Mitsui is also set to acquire 50 percent of the project's rail and port in exchange for future investments, one of the sources said.
Vale said in a statement it was "in continuing negotiations with a potential investor for its coal mining and logistics assets in Mozambique."
It will announce the transaction's details "if and when a deal is reached," Vale said.
Mitsui declined to comment.
Vale executives at an investor event in London Friday said the company would make no further comments on coal at the event. Vale said it would give an update on coal operations Dec. 17.
Vale, which has been hit by a dramatic fall in the price of its key profit driver iron ore, said a year ago it was looking to sell a 15-25 percent stake in its coal assets, spread between Australia and Mozambique.
Analysts at the time valued the coal operations at about $4 billion.
Moatize, one of the largest metallurgical coal mines in the world, was seen as Vale's best asset in the portfolio by far.
Metallurgical coal is used to make coke, a key raw material for steelmaking.
It has not been an easy market in which to find a buyer. Coal prices have declined steadily for more than three years as demand has failed to keep pace with rising production.
Last month European coal futures fell to $69.60 per tonne, their lowest since 2007.
Vale preferred shares, the company's most-traded class of stock, fell 0.4 percent in morning trading in Sao Paulo. Mitsui shares closed up 0.21 percent in Tokyo. (Reporting by Stephen Eisenhammer; Additional reporting by Sarah McFarlane and Eric Onstad in London; Editing by Bernadette Baum)