The European Commission is expected to propose a sixth package of EU sanctions this week against Russia over its invasion of Ukraine, including a potential embargo on buying Russian oil - a measure that would deprive Moscow of a large revenue stream, but that has so far divided EU countries.
Russia supplies 40 percent of EU gas and 26 percent of its oil imports.
To keep the 27-nation bloc united, the Commission may offer Hungary and Slovakia an exemption or a long transition period - with any overall ban likely to be phased in by the year-end, officials said on Monday.
