The European Union energy commissioner and Polish leaders have discussed plans for an EU energy union aimed at greater security at a time of troubled ties with major gas supplier Russia.

Elements of the plan are to be published this month. Poland is urging greater EU energy security through steps like better efficiency, joint gas purchases, sharing of resources and a lesser dependence on imports. The plan has gained urgency amid tensions in ties with Russia over its role in the conflict in Ukraine, a gas transit country.

The EU's Maros Sefcovic met in Warsaw on Monday with Prime Minister Ewa Kopacz and her deputy, Janusz Piechocinski.

Meanwhile, Chevron announced it will no longer explore for shale gas in Poland, a fresh blow to the country's diversification plans.