The company formerly known as Ivanhoe Mines says it has rejected the Mongolian government”s request to renegotiate an investment agreement for the Oyu Tolgoi mine, one of the world”s biggest new copper developments.

Turquoise Hill Resources (TSX:TRQ) said Monday that Mongolia”s mine minister had written to request a renegotiation of a deal signed in October 2009.

However the company, which is majority-owned by Anglo-Australian mining giant Rio Tinto PLC (NYSE:RIO), said it rejected the government”s request — saying the deal is a binding agreement that was re-affirmed as recently as October 2011.

“We have invested nearly US$6 billion, created thousands of jobs for Mongolians and are on the verge of production based on the investment agreement, which provides a stable legal framework and is a legally-binding document,” said Kay Priestly, chief executive officer of Turquoise Hill.

“The investment agreement has been fundamental in building Mongolia”s reputation as an increasingly reliable and secure destination for foreign investment.”

Ivanhoe, which was the driving force behind developing Oyu Tolgoi, changed its name in the summer.