EU-brokered gas talks between Russia and Ukraine on a long-term supply deal due Tuesday in Berlin have been postponed, the EU announced Friday.

"The next round of EU-Russia-Ukraine trilateral gas talks, foreseen to be held in Berlin on Tuesday 14 April has been rescheduled," the European Commission, the EU's executive arm, said in a statement.

"The parties will meet in Brussels at technical level during next week instead," it added.

The goal of the talks, which opened March 20 in Brussels, is to secure Russian gas deliveries for Ukraine through the next winter, as well as onward supplies to Europe.

Russia accounts for about a third of the EU's gas needs, with half that amount transiting via Ukraine

In Kiev, a Ukrainian government source told AFP that "the Russian side refused to be part of these negotiations in Berlin on April 13 so they won't take place."

"The Russians finally refused without giving a reason," the source said.

European Commission Vice-President for Energy Union Maros Sefcovic sounded an upbeat note for the continuation of the talks.

"I welcome the progress that Russia and Ukraine have achieved so far," Sefcovic said in a statement.

"I am confident that expert talks will prepare the ground for the next meeting at political level, which is foreseen to take place still in April," he added.

Russia and Ukraine agreed last week to extend for three months an agreement reached last year to cover winter supplies up to end-March.

The two sides are negotiating against the backdrop of a shaky ceasefire between Kiev government forces and pro-Moscow rebels in eastern Ukraine.