EU foreign ministers met on Monday to debate their response to Russia's arrest of Alexei Navalny and crackdown on demonstrators, as pressure grows to impose sanctions on the Kremlin.

The diplomats from the 27 nations are meeting in Brussels for a busy day of talks ranging from Europe's relations with new US President Joe Biden to efforts to salvage the Iran nuclear deal.

But the arrest of Russian President Vladimir Putin's most prominent critic Navalny and detention of thousands of protesters will be one of the thorniest issues.

"I think the EU needs to send a very clear and decisive message that this is not acceptable," Lithuanian Foreign Minister Gabrielius Landsbergis said as he arrived for the meeting.

European diplomats told AFP that ministers do not expect to agree on sanctions on Monday despite a push from some capitals to take a tough line.

Brussels is expected to hold off until Navalny goes to court in early February to see if the Kremlin puts him behind bars for an extended term.

The anti-corruption campaigner is facing three-and-a-half years in jail for breaching the conditions of an earlier suspended sentence while recovering in Germany from a near-fatal poisoning with a Novichok nerve agent.

His arrest on returning to Russia unleashed a wave of protests on Saturday that saw baton-wielding riot police detain more than 3,500 people.

While sanctions appear unlikely for now, the EU's foreign policy chief Josep Borrell will face pressure to abandon a trip to Moscow pencilled in for next month.

Borrell labelled the arrests a "disproportionate use of force" and wrote on Twitter that Monday's meeting would discuss the EU's "next steps".

Brussels has already hit Russia with sanctions for annexing Crimea and fuelling the Ukraine conflict.

In October, the bloc put six senior Russian officials on an assets freeze and travel ban blacklist over the "assassination attempt" on Navalny.

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