The impasse between Rio Tinto and the Mongolian government over the Oyu Tolgoi copper mine could be resolved by September, Reuters reported.

A government official told Reuters that underground mining will begin within two years.

Rio Tinto halted construction on the mine last year after the government said financing had to be approved by parliament because it was concerned cost over-runs would delay when the country began receiving its share of profits.

But Mongolia's vice minister for economic development, Chuluunbat Ochirbat, said the government had learned from its mistakes and progress was now being made.

"We are under arrangements and negotiations with Rio Tinto now to complete the process by September this year," he said. "Underground mining will be put into operation in a year and a half or two years time."

Openpit mining has already started at the site, but the real step-up in production requires mining to move underground. The stakes are massive with the mine potentially accounting for 20-30 percent of Mongolia's economy.

The Mongolian government owns 34 percent equity in the copper mine, while Rio Tinto owns 51 percent of Canadian company Turquoise Hill which has the remaining 66 percent stake in Oyu Tolgoi.