Ratings agency S&P Global further downgraded Russia's credit rating to 'junk' as new international sanctions imposed and the country's protective measures increased the risk of default.

S&P downgraded the sovereign rating to CCC-minus from BB-plus less than a week after downgrading it from investment grade.

The downgrade follows the introduction of measures that, in our opinion, will significantly increase the risk of default, the agency said in a statement.

S&P said new G7 restrictions and capital controls imposed by the Russian government to protect the ruble could limit the country's ability to repay its debt. The rating agency also warned of a further downgrade.

Ratings agencies Fitch and Moody's also downgraded Russia by six notches, saying Western sanctions have cast doubt on Russia's ability to service its debt and will weaken the economy.