The agreement by ambassadors from the 28 European Union nations meeting in Brussels will be formalised by foreign ministers from the bloc when they meet next week, the officials said.
"EU foreign ministers will finalise the decision in Luxembourg on Monday," Poland's permanent representative to the EU said on Twitter, while several sources also confirmed the agreement.
The following day, the foreign ministers of France, Germany, Ukraine and Russia are slated to hold talks in Paris, it was announced today. It is hoped those meetings may create renewed diplomatic momentum towards resolving the violence in east Ukraine, and address tensions between Russian and Western nations over the conflict and sanctions that have arisen from it.
The United States has also imposed economic sanctions on Russia.
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In March, EU leaders agreed in principle to roll the sanctions over by linking them directly to Russia's full implementation of a February ceasefire brokered by France and Germany in Minsk that runs to December this year.
"This is just putting into effect the March summit decision," one EU source told AFP.
"The idea is to extend them to end-January to give time to review progress on the Minsk accord before having to take a new decision."
EU leaders meeting on Thursday and Friday in Brussels will then make the formal announcement, sources said.
The sanctions extension will keep relations between Russia and the West in the deep freeze, a year and a half after the crisis in Ukraine triggered the worst rift since the Cold War.
NATO chief Jens Stoltenberg on Tuesday accused Russia of "dangerous" nuclear sabre-rattling after President Vladimir Putin announced plans to deploy 40 new nuclear ballistic missiles.
Russia says the move is in response to the US-led NATO military alliance increasing its presence in east European states once ruled from Moscow.