European Commission President Jose Manuel Barroso said future trilateral talks with Kiev and Moscow would focus on energy and national security issues.

Barroso said he spoke by phone with Russian President Vladimir Putin to discuss the overall context of the situation in Ukraine.

Ukraine and Russia have historic differences over natural gas. Russian energy company Gazprom in 2006 and 2009 cut gas supplies through Ukraine, jeopardizing downstream supplies to Europe, in response to contractual woes. That problem was exacerbated when in late 2013 Ukraine, a former Soviet republic, started tilting toward the European Union through an association agreement.

"It was agreed to hold consultations between the presidents of Russia, Ukraine and the European Commission on the issues related with the implementation of the association agreement as well as on the supply of gas, in parallel with the efforts to stabilize the political and security situation," Barroso's office said in a Thursday statement.

Russia is Europe's top natural gas supplier and the bulk of those supplies run through Ukraine's pipeline system, which was built in the Soviet era.

Barroso's office offered no time frame for the talks. Russia has suggested a September date.