Gazprom head Alexei Miller said Friday that the state-owned gas giant could retaliate against European countries if they were to sell its gas back to Ukraine through large-scale reverse gas flows, according to Moscow Times.

“There is no physical reverse flow, but if we detect a reverse flow on gas-measuring stations in Europe, we may impose restrictions”, Miller said.

Moscow cut off supplies to Kiev in mid-June after Ukraine and Russia failed to reach an understanding regarding debt payments, disagreements about tariffs and Ukraine signing an association agreement with EU. Gas deliveries to Europe via Ukraine are not affected.

Ukraine proposed to EU to buy back some Russian gas from them. In late April, Ukraine and Slovakia signed a reverse flow agreement that would make use of an old, unused pipeline to begin importing Russian gas from Slovakia to Kiev.