Dozens of Greenpeace demonstrators chained themselves outside Neste Oil headquarters near Helsinki on Tuesday in protest at the company's palm oil production for diesel fuel.

"Fuel manufacturing that requires more and more cultivation areas for raw materials (like palm oil) is a bad investment (that leads to) forest destruction," Maija Suomela, in charge of Greenpeace's palm oil protests, said in a statement.

Around 30 activists blocked the entrance to Neste Oil's headquarters in Espoo with a sheet of plywood early Tuesday, chaining themselves to the door and windows and holding up placards stating "Bad investment," according to public broadcaster YLE.

Greenpeace demanded that Neste Oil, which earlier this year opened the world's biggest renewable diesel plant in Singapore based largely on palm oil production in Indonesia and Malaysia, reveal the composition of its NexBTL diesel fuel.

The environmental group also called for the company to reveal where its raw material came from.

Neste Oil spokesman Osmo Kammonen told AFP the company agreed there should be a ban on felling rain forests, insisting "we are heading in a direction where we use more (raw materials) which don't require as much land use as the current ones."

"But even with the current ones I am convinced that we have a very sustainable supply chain," he said, adding that Neste was in a "continuing dialogue" with Greenpeace.

Neste, which last month opened Europe's largest renewable diesel plant in Rotterdam, announced its third quarter results Tuesday showing it had produced 200,000 tonnes of the renewable fuel between July and September.

It has said it aims to increase its renewable diesel production to 2.4 million tonnes next year, but denies Greenpeace allegations that this will lead to the cutting of more rain forests to make room for palm oil plantations.

"The share of palm oil is going down," Kammonen said, adding that the oil would account for less than 50 percent of bio-based raw materials this year and going forward.