Booming developing world demand was already pushing up the price of basic food items when Russia was hit by a catastrophic drought that eventually forced the Kremlin to call a halt to all wheat exports last year.

But the emergency measure provided only temporary relief, with both shoppers and analysts noting an alarming new trend developing on the shelves of stores stretching from Vladivostok in Russia's Far East to Kaliningrad near Poland.

"Since the summer, potatoes have become unaffordable," said 30-year-old Marina, a regular shopper at the Moscow market.