Rio currently has an ‘A3' senior unsecured rating.

"The review results from the strengthening Rio Tinto's metrics attributable to its debt reduction in recent years under its liability management program, the reduction in costs from the group's focus on productivity and logistics, which helps to mitigate cost creep being seen in input costs," Moody's said.

"A recovery in prices over 2017 and 2018 has also benefitted the company."

Moody's said the review would consider Rio's asset base, commodity diversification, cost structure, and strategic growth objectives.

"Given the volatility in the key markets in which the group participates, the review will also assess credit metrics and cashflow at the low end of our price sensitivities to determine the resilience of the group's performance through different price points," it said.

"A further focus of the review will be the group's commitment to a single A financial policy with a strong discipline in capital investments and M&A activity."

The review comes after Moody's upgraded BHP's ratings last week from A3 to A2 with a stable rating.