Russia’s sovereign credit rating has been cut by six notches to "junk" status by Moody’s and Fitch after the ratings agencies said they were uncertain the country could service its debt.

The country’s long-term foreign currency issuer default rating was downgraded by Fitch to B from BBB, while Moody's lowered its long-term issue and senior unsecured debt ratings for both local and foreign currency from Baa3 to B3.

Both Moody’s and Fitch placed them under review for further demotion, citing recent sanctions as a major hit to economic growth, as well as ongoing domestic and geopolitical uncertainty.

Fitch, which also downgraded 10 Ukrainian companies, said the only other precedent to such a large downgrade on a single sovereign entity was South Korea in 1997.

"The severity of international sanctions in response to Russia's military invasion of Ukraine has heightened macro-financial stability risks, represents a huge shock to Russia's credit fundamentals and could undermine its willingness to service government debt," Fitch said in its report.

"The sanctions could also weigh on Russia's willingness to repay debt. President Putin's response to put nuclear forces on high alert appears to diminish the prospect of him changing course on Ukraine to the degree required to reverse rapidly tightening sanctions,"

Read more: Explainer: How economic sanctions work

Meanwhile, Moody’s said: “The significant concerns around Russia's willingness to service its debt are a reflection that Russia's institutional strength has very materially weakened with increasing evidence that the executive faces few checks and balances.”

It also follows a similar move by S&P, who lowered Russia's rating to junk status last week.

Russia's financial markets have faced mounting turmoil amid sanctions imposed by the West over its invasion of Ukraine, the biggest attack on a European state since the Second World War.

Goldman Sachs (GS) have forecast that the Russian economy could shrink by 7% this year, which would plunge it into a deeper recession than the one caused the COVID-19 pandemic.

On Thursday, the London Stock Exchange (LSEG.L) suspended trading in 27 more companies with strong links to Russia.

Trading in energy giants such as Lukoil (LKOH.L), Gazprom (OGZD.L), EN+ (ENPL.L), and Rosneft (ROSN.L) has been suspended, alongside Russian bank Sberbank (SBER.L), Novolipetsk Steel (NLMK.L), and Polyus (PLZL.L).

The move comes into effect immediately and follows similar actions from other indexes. On Monday the Deutsche Borse halted trading in 16 companies with links to Russia, while the New York Stock Exchange and Nasdaq followed suit.

Read more: London Stock Exchange blocks 27 companies with Russian ties

The Russian rouble plummeted to fresh record lows on the back of the news on Thursday, falling more than 10% against the dollar.

It is now trading at 117.5, the first time it has traded above 110 on the Moscow Exchange. It also shed 7% against the euro.

Russia’s central bank has imposed a number of restrictions designed to prop up its faltering economy, including a 30% commission on foreign currency purchases by individuals on currency exchanges.

Brokers said this appeared to be designed to curb demand for the dollar, however, it did little to halt the rouble's slide on Thursday.

Watch: Ukraine war: Russians wait in queues for cash as rouble plunges and hyperinflation looms