Gazprom claims maintenance is behind the shortfall, as it is accused of penalising Poland over supplying gas to Ukraine

A decision by Russia to cut gas exports to Poland without warning has rekindled fears about Europe's reliance on Siberian gas at a time of increasing tension between Moscow and the west.

The Polish state energy group, PGNiG, said it was trying to find out why volumes had been slashed by up to 24% when it had been exporting gas itself to Ukraine to make up for Russian shortfalls there.

Its counterpart in Kiev, Ukrtransgaz, accused Kremlin-controlled Gazprom of penalising Poland and undermining onward gas supplies to Kiev.

"Today Russia started limiting gas supplies to Poland in order to disrupt the reverse (flows) from Poland that we receive ... Poland stopped reverse supplies to Ukraine in the range of 4m cubic metres," said Ihor Prokopiv, chief executive of Ukrtransgaz, according to the Russian news agency, RIA.

Mutual suspicions are higher than at any point since the collapse of the Soviet Union, following the conflict in Ukraine and western accusations that Russia has augmented the rebellion in the east with its own troops. Moscow denies the claim.

Nato last month estimated that more than 1,000 Russian soldiers were operating covertly in Ukraine, as part of a separatist effort to roll back advances by Kiev.

Earlier Ukraine's president, Petro Poroshenko, said most Russian troops had now been withdrawn. "According to the latest information I have received from our intelligence, 70% of Russian troops have been moved back across the border," he said. "This further strengthens our hope that the peace initiatives have good prospects." Poroshenko said parts of east Ukraine would be given special status. But Ukraine would remain a sovereign and united entity, under a peace deal agreed in Minsk last Friday. But Ukrainians are anticipating a difficult winter ahead, reliant as they are on Russian gas to power their economy and heat their homes.

Nick Perry, a British energy consultant, said that it was not surprising that Gazprom's actions had prompted a nervous response. "Since the 1990s, the International Energy Agency (IEA) has been investigating how Europe would survive if they lost some of its biggest sources of gas for six months. People have been looking at this for a long time."

But Gazprom sources insisted the shortfall could be attributed to maintenance work that was going on fields and pipelines ahead of the important winter season when demand is at its highest.

A statement from the group sidestepped the issue by saying it was pumping gas to all destinations "according to the resources available for exports and for the continuing pumping to storage facilities in the Russian Federation".

Jonathan Stern, a gas expert at the Oxford Institute for Energy Studies and a member of the EU-Russia Gas Advisory Council, believed there was more likely a technical, not a political problem.

"If Gazprom wanted to punish the Poles then it would not do so surely when the weather was warm and in breach of its contractual obligations," said Stern who met the Russians for a gas summit in Vienna this week. "The Russians are acutely aware that any (commercial) moves at this time will be interpreted in the worst possible light (by the west)."

But energy has been at the centre of previous conflict. Gazprom cut off gas to Ukraine in June arguing that Kiev had not paid its bills but the move was interpreted in the west as an attempt to destabilise its southerly neighbour. Similar boycotts by Gazprom against Ukraine – usually in the middle of winter – have been imposed against Ukraine and others in the past decade.

The latest upset comes as the European Union has drawn up deeper sanctions against Russia over its support for separatist rebels who have taken over parts of eastern Ukraine.

Slovakia, a major hub for Russia gas exports to Europe, said volumes were steady on Wednesday, and operators in Hungary, Bosnia and Serbia said there was no disruption to their supplies.

Igor Gorsky, a spokesman for Gazprom Transgaz Belarus, the Gazprom subsidiary that operates export pipelines via Belarus, said: "There have been no extraordinary situations from our side, or any maintenance work, which could have an impact on supply volumes."

Political relations between Warsaw and Moscow are particularly bad. Poland has lobbied the EU hard to impose tougher sanctions on Moscow, and it is to host elements of a new Nato rapid reaction force, created in response to the Russian intevention in Ukrainer.

Gazprom supplies a third of Europe's gas and for many EU countries it is the main source of power for homes and industry but the Russian firm is a big revenue earner for the Kremlin and any volume cuts would damage the company and country financially.