Ivanhoe Mines and Rio Tinto have formally told the Mongolian government they are not prepared to renegotiate an investment agreement for the Oyu Tolgoi gold and copper mine, which is under construction.
The companies also wrote to members of Mongolia's National Security Council asking for help to ensure the government's "full and immediate" support for the deal.
Last week, Ivanhoe received a letter from a representative of the Mongolian Cabinet asking the company and Rio Tinto, which owns a 49-per-cent stake in Ivanhoe, to discuss potential changes to the investment agreement.
The changes sought include an ability for the Mongolian government to increase its stake in the mine and the application of a sliding-scale royalty to the project.
The investment agreement was signed by the Mongolian government, Ivanhoe and Rio Tinto in October 2009 and may be amended only by mutual consent of all three parties.
Toronto-listed Ivanhoe Mines holds a 66-per-cent interest in the project, while the Mongolian government holds 34 per cent.
Rio Tinto owns 49 per cent of Ivanhoe and is managing construction of the Oyu Tolgoi mining complex.
The project, which is 50 per cent complete, is on track toward production of its first ore next year and commercial production of copper, gold and silver concentrate in the first half of 2013.
Oyu Tolgoi is expected to produce 1.2 billion pounds of copper and 650,000 ounces of gold per year in the first decade of operation.
Rio Tinto is one of the world's major suppliers of aluminium, copper, diamonds, thermal and metallurgical coal, uranium, gold, industrial minerals.
In addition to its stake in Oyu Tolgoi, Ivanhoe holds a 57-per-cent interest in Mongolian coal miner SouthGobi Resources, 54-per-cent stake in Ivanhoe Australia and a 50-per-cent interest in Altynalmas Gold Ltd., a private company developing a gold project in Kazakhstan.