TIRANA, ALBANIA - The United States has encouraged Serbia and EU-member Slovenia to diversify their energy sources away from Russian gas to make sure any potential disruptions will not hurt their economies, a senior U.S. official said Friday.

Wrapping up a tour of Slovenia, Serbia, Kosovo and Albania, Mary Burce Warlick, the Principal Deputy Assistant Secretary of State for Energy Resources, said she urged them to look at ways to strengthen their energy security by diversifying its sources.

Warlick said the United States believes energy security issues in Europe are very important and "really fundamental to national security issues more broadly."

Serbia, a candidate to join the European Union, relies almost exclusively on Russian gas supplies while Slovenia imports less than half of its gas from Russia while Albania and Kosovo, both staunch U.S. allies, import no gas from Russia.

"I sensed a real openness on the part of really all countries with whom we engaged to try to identify those solutions, partnering with Europe and us and many others to try to find a way to achieve some of those solutions," Warlick said.

Warlick, a former ambassador to Serbia, said the United States had been discussing energy diversification with a number of European countries that rely on Russian gas.

The cutoff of Russian gas from Ukraine in 2009 drove home the importance of diversification in European capitals.

"Our approach has been not to say that Russian gas shouldn't remain as it does an important part of the energy equation in Europe, but simply for all countries to think a little bit again on how they position themselves to better diversify their energy mix," she told Reuters in an interview in Tirana.

The United States has suggested either new investment or connections with neighboring countries that will enable them to consider "developing a more diversified mix of gas on the one hand but also look to develop other resources," Warlick said.

They could tap into additional volumes of gas that might come online in 2020 when the TAP pipeline brings Azeri gas to Europe, as well as from increasing volumes of LNG thanks to LNG terminal projects in and around Europe, she said.

"I think the reform measures that have taken in many countries are going to pave the way for increased investment, including in the energy sector," Warlick added.