EU regulators will announce on Wednesday anti-trust charges against Russia energy giant Gazprom, sources close to the matter told AFP.

The European Commission formally opened its probe in September 2012 and has significantly delayed moving forward due to tensions with Moscow over the crisis in Ukraine.

The EU will officially complain that Gazprom was hindering competition in Central and Eastern European gas markets, where the company benefits from a dominant position.

Ricardo Cardoso, a commission spokesman, refused to comment on the matter.

Gazprom's leading position and close ties to the Russian government has made the handling of the case especially sensitive for EU regulators.

The complaint against Gazprom will come a week after the EU's Competition Commissioner Margrethe Vestager formally charged Google with abusing its dominant position, in another high profile case.

Gazprom's repeated disputes with Ukraine led to the company suspending gas supplies on several occasions and has become a crucial aspect of conflict between the Western-backed government in Kiev and pro-Russian rebels in eastern Ukraine.

The probe comes as the EU is also helping to broker a shaky ceasefire between Kiev government forces and the pro-Moscow rebels.