Mountainous and remote, the Greek-Bulgaria border once formed the southern corner of the Iron Curtain. Today, it's where the European Union is redrawing the region's energy map to ease its heavy reliance on Russian natural gas.

A new pipeline — built during the COVID-19 pandemic, tested and due to start commercial operation in June — will ensure that large volumes of gas will flow between the two countries in both directions to generate electricity, fuel industry and heat homes.

The energy link takes on greater importance following Moscow's decision this week to cut off natural gas supplies to Poland and Bulgaria over a demand for ruble payments stemming from Western sanctions over the war of Ukraine.

The 180-km (110-mile) project is the first of several planned gas inter-connectors that will allow eastern European Union members and countries hoping to join the 27-nation bloc access to the global gas market.

In the short term, it's Bulgaria's backup.

The pipeline connection will give the country access to ports in neighbouring Greece that are importing liquefied natural gas, or LNG, and also will bring gas from Azerbaijan through a new pipeline system that ends in Italy.

It's one of many efforts as member states scramble to edit their energy mix, with some reverting back to emissions-heavy coal while also planning expanded output from renewables.

Germany, the world's biggest buyer of Russian energy, is looking to build LNG import terminals that would take years, and Italy, another top Russian gas importer, has reached deals with Algeria, Azerbaijan, Angola and Congo for gas supplies.

The European Union wants to axe its dependence on Russian oil and gas by two-thirds this year and completely over five years through alternative sources, wind and solar, and conservation.

Russia's invasion of Ukraine is likely to accelerate changes in the EU's long-term strategy, adapting to energy that is more expensive but also more integrated among member states, said Simone Tagliapietra, an energy expert and research fellow at the Brussels-based think tank Bruegel.