Mongolia has asked Rio Tinto, its partner in the huge Oyu Tolgoi copper and gold mine in the Gobi desert, not to further increase its estimated USD 7.06 billion budget for the project’s expansion, its mining minister told Reuters.

The two partners have only just ended a long-running tussle over the underground expansion of the mine, which is behind schedule and over budget, with Rio last year agreeing to waive USD 2.4 billion in debt owed to it by the government and commit to a structure that did not require additional loan financing.

Costs to expand the facility have ballooned from an original estimate of USD 5.3 billion in 2016, raising friction over funding.

“The government has asked Rio Tinto to not increase the budget,” J.Ganbaatar, the minister for mining and heavy industries, told Reuters on Jan. 16 in a video interview. Rio Tinto declined to comment.

Mongolia owns 34 percent and Anglo-Australian miner Rio Tinto 66 percent of Oyu Tolgoi, one of the world’s largest known copper and gold deposits, which is slated to eventually produce more than 500,000 tonnes of copper a year.

The minister added that he expects first production from the underground mine by mid-2023 as scheduled. The facility, Rio’s biggest copper growth project, began open-pit mining in 2011.

Though they have been cushioned by strong commodity prices, mining companies have warned that high inflation will remain a challenge this year, keeping costs from energy to explosives and equipment high, and possibly hitting short-term demand.