Russia's fast-growing foreign exchange reserves have climbed to just under $400 billion, sparking concern among domestic officials about a spike in inflation.

Russia's gross international reserves climbed $8 billion to $394.3 billion in the week ending May 18, the country's central bank said Friday.

"The scale of this reserve growth and the consequent increases in the money supply is getting the authorities seriously worried," said Al Breach, head of research for Russia at UBS Investment Research, in a research report.

Anna Zadornova, analyst at Goldman Sachs European Economics Research, estimates that there were $6.7 billion net private inflows during the week, bringing the total for the year to $58.8 billion, much higher than the $41.6 billion that flowed into the country in all of 2006.

Consumer prices (CPI) rose 7.6% year-on-year in April compared with 7.4% in March, while producer prices (PPI) posted a sharper increase, likely boosted by higher oil prices and the stronger euro. PPI surged 7.6% year-to-date in April from 3.1% in March and above market expectations of around 5.8%.