Greece's retailers association on Monday reported a 12.7 percent drop in sales over the last three months year-on-year, as government capital controls take their toll on customers' spending.

A study by the association said turnover for June, July and August "will not exceed 9.25 billion euros ($10.36 billion), against 10.5 billion a year ago".

In June, "losses reached 305.4 million euros" -- a five percent fall since a year earlier -- with losses then accelerating over the next two months. Takings plunged 14.9 percent and 17.3 percent in July and August respectively, according to the study.

The radical-left government of Alexis Tsipras, who quit as prime minister on August 20, triggering snap elections, imposed a raft of capital controls at the end of June in a bid to prevent a catastrophic bank run.

While some of the capital controls have since been relaxed, Greeks remain unable to withdraw more than 420 euros ($471) a week from ATMs, dampening retail spending.

Cash withdrawals totalled 1.5 billion euros nationwide in July, according to figures from the Bank of Greece -- the lowest since November 2014.

Since December, bank withdrawals have fluctuated between two billion and 12 billion euros a month, the bank said.