A Russia-Ukraine gas dispute last January cut supplies to Europe
Russia has warned that a price dispute with Ukraine could cause it to cut oil deliveries to three EU countries, Slovakia has said.
Energy deliveries to Slovakia, Hungary and the Czech Republic would be disrupted by the cut, it added.
The Slovak government said it had received the warning via the European Union, which said it had been informed of the possible cut by Moscow.
The country's security council has met to discuss the warning.
Slovak Prime Minister Robert Fico and Economy Minister Lubomir Jahnatek are expected to hold a news conference about the emergency meeting.
Brussels was monitoring the situation, an EU official said, adding that there was no cause for concern as the three EU countries potentially affected had sufficient reserves.
Russia had announced "the possibility of suspending oil supplies to... Slovakia, Hungary and the Czech Republic", Slovakia's government said, quoting a letter from the European Commission.
"The reason is allegedly unresolved problems between the Russian Federation and Ukraine concerning oil transit."
Nikolai Tokarev, head of Russian pipeline company Transneft, was quoted by the Reuters news agency as saying Ukraine had demanded higher payments for the transit of Russian oil.
Moscow agreed to ease the terms under which it supplies gas to Ukraine last month after talks between Russian Prime Minister Vladimir Putin and Ukraine's Yulia Tymoshenko.
Moscow said that deal should prevent disruption - last January, many countries in Europe were left short of gas due to a payment dispute between Moscow and Kiev.
Russia provides about a quarter of the gas consumed in the EU and 80% of that is piped through Ukraine.