File picture: Nic Bothma/EPA

Johannesburg - Ratings firm Moody's said on Wednesday it was placing South Africa's state power firm Eskom's credit rating on review for a downgrade.

It cited the risk of the country's institutional, economic and fiscal strength deteriorating after President Jacob Zuma dismissed a respected finance minister last week.

On Monday, S&P cut South Africa's credit level to junk status over growing concerns of political and policy instability following Zuma's midnight cabinet reshuffle last Thursday.