Russia's joint exercises with ally Belarus and other drills near Ukraine have fanned fears Russia may be poised to invade Ukraine, something Moscow has repeatedly denied planning
The EU official said US talks with Russia were "not yielding a lot" but that dialogue with President Vladimir Putin was still open through the leaders of Germany and France.
The official, who spoke under condition of anonymity, said the harsher the EU sanctions against Russia would be in case of a military invasion, the bigger the hit for the bloc should Moscow retaliate.
The official said 40 per cent of EU gas came from Russia and that the bloc was in talks with Norway and Qatar, among others, about increased energy supplies if needed.
The official also said the EU was looking at how quickly Russia could switch its energy supplies to China should it cut sales to Europe.
The EU was also preparing for refugee arrivals should Russia invade Ukraine, they said.
The source said the EU was expecting to decide on further macroeconomic support for Ukraine and that Kyiv was seeking more political support.
Some in the EU wanted to impose strong sanctions to discourage Russia from any attack, but others said that would amount to an escalation of tensions and that the bloc should only react later if needed, the official said.
Russian Defence Minister Sergei Shoigu on Monday told President Putin that some of the country's military drills had already ended and others were coming to a close.
Also on Monday, Russian Foreign Minister Sergei Lavrov suggested to President Putin that Moscow continue along the diplomatic path in its efforts to extract security guarantees from the West, as tensions soar over Ukraine.
Lavrov told Putin the United States had put forward concrete proposals on reducing military risks, but said responses from the European Union and NATO military alliance had not been satisfactory.
