Rio Tinto has reduced its exposure to tax havens over the past year but its Singapore marketing hub continues to be investigated by the Australian Taxation Office.

The resources giant said 17 of its 600 subsidiaries were domiciled in tax havens, and eight of those were dormant.

Rio said five of the remaining nine were acquired through acquisitions, and turnover had been reduced in others.

Rio Tinto paid $US4.5 billion in tax in 2015. Photo: Louie Douvis

The exposure to tax havens is down from the previous year, when 20 Rio subsidiaries were located in such nations and only two were dormant. 

Rio considers a tax haven to be a jurisdiction with a corporate tax rate below 10 per cent.

The declaration was made in Rio's annual "taxes paid" report, and comes after Rio confirmed last year that its Singapore office was being scrutinised by Australian tax officials.

The company said negotiations with the ATO were ongoing.

"We are engaged in discussions with the ATO in relation to the pricing of iron ore marketing services," the company said.

The taxes paid report revealed that Rio's tax payments had fallen in line with commodity prices.

The company paid $US7.1 billion in taxes and royalties to governments around the world in 2014, but that fell to $US4.5 billion in 2015.

 Australia continues to get the lion's share of Rio's tax and royalty payments, with $US3.3 billion to flowing to Australian governments in 2015, down from $US5.7 billion in 2014.

The Federal and Western Australian governments received the biggest share of that spend.

Mongolia, which is home to Rio's Oyu Tolgoi copper project, was one of the few nations where Rio's tax spend increased year on year.

The company paid $US278 million in the developing nation in 2015, up from $US185 million in 2014.

Only Australia and Canada received more tax payments from Rio in 2015.

A significant portion of the taxes paid in Mongolia related to withholding tax on loans for the $US5.3 billion underground expansion of the copper, gold and silver mine.

The European Union has demanded resources companies provide more transparency about their payments to governments in recent years, and similar demands have come from regulators in Canada and the US.

The ATO introduced a voluntary code for companies to report their tax payments in 2015.

"At a time when tax and transparency continue to be seen by the public as important topics of discussion we are proud to produce this report. Debates about tax rates and contributions are best served when factual information is provided. This is what we have set out to do with our annual taxes paid reports," said Rio's chief financial officer Chris Lynch.

But while Rio has been considered a leader in tax transparency and has supported the development of many of those transparency codes, the company warned that the growing number of transparency schemes could become problematic.

"We are concerned about the proliferation of such new initiatives," the company said in the report.

"Potentially we will face multiple and inconsistent reporting requirements, and will incur significant additional costs in complying with these obligations, often with little or no added public benefit."

The release of the report comes just days before Jean Sebastien Jacques officially replaces Sam Walsh as chief executive of Rio.

The leadership transition has come during a period of surprisingly high prices for Rio's most important product, iron ore.

Prices for the steelmaking ingredient were expected to struggle in 2016, but have spent most of the past five months above $US50 per tonne, and the bulk commodity was worth $US53.86 per tonne on Tuesday.