Italy has joined Russia in condemning Ukraine for allegedly stealing Russian gas intended for European consumers.
Italy, like much of Europe, is in the throes of a cold snap
Italy receives Russian gas through pipelines across Ukraine, but is reporting continuing shortfalls in supplies as it endures a cold snap.
Industry minister Claudio Scajola said it was "inadmissible" for Ukraine to take gas meant for his country.
Ukraine has strongly denied that it is siphoning off Russian gas in transit for Europe.
It insists it is adhering to agreements it has previously signed with Russia.
Mr Scajola's comments come amid a growing debate in Europe about the continent's dependence on Russian energy.
Energy officials from eight central and eastern European countries have called on the EU to help build an integrated gas storage and distribution network to reduce reliance on Russia.
A package of measures is being discussed, including the Nabucco project - a proposed 3,000km (1,850 mile) pipeline to take Iranian and Azeri gas from Turkey to Austria, through Bulgaria, Romania and Hungary.
Until now, only Russia has held Ukraine responsible for the supply problems.
The BBC's Steven Eke says that if Italy's condemnation marks the start of a reassessment of who is to blame for the problems, Ukraine could find itself in a very difficult position.
After talks in Moscow, Mr Scajola said he wanted Russia to pay particular attention to all contracts and responsibilities for delivery of Russian gas to his country.
Italy, which relies heavily on Russian gas, says deliveries are falling below the expected level for a second week now.
Mr Scajola's Russian counterpart Viktor Khristenko criticised Ukraine for "unsanctioned siphoning" and said Moscow was doing everything to guarantee supplies to Italy.
Poland, Hungary and Turkey have also complained of reduced deliveries of Russian gas.
European countries first experienced problems with gas earlier in the month, when Russia suspended supplies to Ukraine as a result of Kiev's refusal to agree to a fourfold price hike.
The two neighbours have twice delayed the signing of a controversial compromise deal agreed after the crisis.