KIEV, Sept. 20 - Moody's Investors Service cut Ukraine's sovereign credit rating further into junk category on Friday and warned that more downgrades could come.

Moody's cut the rating by one notch to Caa1 from B3, with the outlook placed on review for downgrade, as it cited concerns over a drop in foreign currency reserves, new debt issuance and potentially worsening relations with Russia.

Ukraine is rated B with a negative outlook by both Standard & Poor's and Fitch Ratings.

"The country's foreign-exchange reserves are already at a very low level and pressure on reserves is likely to rise due to increased domestic demand for foreign currency in the autumn and significant foreign-currency-denominated debt repayments until end-2014," Moody's said in a statement.