BUCHAREST (Reuters) - Thousands of Romanians rallied outside the country's top court on Friday to protest against the December cancellation of the presidential election in which a little-known pro-Russian candidate won the first round.

Although small, protests have been continuing since Dec. 6, when the Constitutional Court voided the election two days before the second round. Its move came after state documents showed frontrunner Calin Georgescu had benefitted from an unfair social media campaign likely orchestrated by Russia.

Moscow denied any interference in Romania's election.

The decision to cancel the presidential election further weakened public trust in state institutions, polarised voters angered by mainstream parties’ political infighting and graft allegations and strengthened hard right and ultranationalist parties, which now hold over a third of parliamentary seats.

Georgescu's lawyer filed a request on Friday for the Constitutional Court to reinstate the election result. Georgescu, who was not present, urged his supporters to join in.

Roughly 4,000 supporters gathered outside the court with a mock coffin emblazoned with the word "Democracy".

They waved national flags, carried Christian icons and pictures of Georgescu, and chanted "We want to vote" and "Bring back the second round".

Romania's ruling coalition agreed this week to rerun the two-round presidential election on May 4 and May 18, nearly six months after the cancelled vote.

Outgoing President Klaus Iohannis, whose term expired on Dec. 21, will stay on as head of state until his successor is elected.

It remains unclear whether Georgescu, who is critical of NATO and opposes Romanian support for Ukraine against Russia’s invasion, will be allowed to run for president again.

Romania has the longest land border with Ukraine of any European Union and NATO member state. It has helped export millions of tons of Ukrainian grain through its Black Sea port of Constanta, trained Ukrainian fighter pilots and donated a Patriot air defence battery to Kyiv.

(Reporting by Luiza Ilie and Octav Ganea; Editing by Gareth Jones)