Finance ministry said on Saturday the ratings downgrade by Moody's and Fitch will increase the country's borrowing costs and constrain its fiscal framework.

"The decision by Fitch and Moody's... is a painful one," Tito Mboweni, Minister of Finance, said in a statement.

There is an urgent need for government to implement structural economic reforms to avoid further harm to the country's sovereign rating, he said.

Credit rating agencies Fitch and Moody's lowered the sovereign ratings further into junk late on Friday on rising debt and more likely weakening in the fiscal strength, while S&P Global affirmed on hopes that credit strength will offset them.