LONDON — Europe's united front against Moscow is being put to the test as countries struggle to agree a ban on Russian oil imports.

European Union diplomats failed to reach consensus Sunday on the terms of an embargo, but were holding further talks Monday in a bid to present a deal for approval by EU leaders at a summit later in the day.

A senior EU diplomat told CNN that the bloc was "in the last stretch" of agreeing the terms of an oil embargo, but needed more time to convince some member states, including Hungary, to come on board.

"We do understand their special situation, we do understand their security of supply problem, we do understand their search for assurances to be able to solve that," the diplomat said.

European officials first proposed joining the United States and others in banning Russia's oil a month ago as part of a sixth package of EU sanctions over the country's invasion of Ukraine. But an agreement has been held up by the reluctance of some countries that are particularly reliant on Russian crude delivered via pipeline.

There may now be a way forward. EU leaders could agree to ban all Russian oil by the end of this year, but provide a temporary exemption to imports via pipeline, according to a draft of the summit conclusions viewed by Reuters.

Europe is the biggest buyer of Russian energy. Russian crude accounted for 27% of the bloc's imports in 2021, according to Eurostat. That's around 2.4 million barrels per day, data from the International Energy Agency shows. About 35% of that was delivered via pipelines to the bloc, according to the IEA.

But pipeline deliveries made up a much bigger share of Russian oil shipments to Hungary (86%), the Czech Republic (97%) and Slovakia (100%).

Earlier this month, Hungary's Foreign Minister Péter Szijjártó likened the EU's proposals for a complete ban on Russian oil to an "atomic bomb" for his country's economy. Its government has previously said it would need a minimum of three to five years to cease all imports.

Care must be taken, however, to ensure any exemptions do not unfairly benefit some countries over others, the senior EU diplomat told CNN.

"We have to be really careful in the legal sanctions text, that we preserve the [EU] internal market everywhere, and that we preserve the level playing field," the diplomat said.

Europe has thus far maintained a united front against Russia over the war in Ukraine, imposing round after round of economic sanctions, which included an embargo of its coal imports. It is also aiming to slash imports of Russian natural gas by 66% by the end of this year.

But cracks have started to appear in recent weeks as soaring inflation and sluggish growth batter Europe's economies.

"I am very worried about what a recession in Europe would do to European resolve to stick with it and continue to escalate the sanctions," Jason Furman, a Harvard professor who previously served as President Barack Obama's top economic adviser, told CNN Business at the World Economic Forum in Davos last week. — CNN