By Mark Trevelyan

LONDON (Reuters) -The head of Russia's only independent election watchdog was sentenced on Wednesday to five years in a penal colony after being found guilty of working with an "undesirable organisation".

Grigory Melkonyants, co-chair of the Golos movement, was arrested in August 2023. He pleaded not guilty at his trial.

Human rights campaigners say the case against the 44-year-old is part of a wider crackdown on civil society that has intensified since Russia's full-scale invasion of Ukraine in February 2022.

News outlet Mediazona said Melkonyants called out to supporters in the courtroom and urged them not to be downhearted over the verdict.

Golos, which means both "voice" and "vote" in Russian, first angered the authorities by publicising evidence of what it said was fraud in a 2011 parliamentary election that led to opposition protests, and then in the presidential vote that returned Vladimir Putin to the Kremlin for a third term in 2012.

The charges against Melkonyants were based on his alleged involvement with the Montenegro-based European Network of Election Monitoring Organisations, which links watchdogs in former communist countries in Europe and Central Asia. ENEMO did not immediately respond to a request for comment.

Golos says it has had no interaction with ENEMO since Russia banned the latter as "undesirable" in 2021.

"This absurd case (against Melkonyants) defies easy explanation, not only for foreigners but even for ourselves," Golos co-chair Stanislav Andreichuk told Reuters.

Despite being designated as a "foreign agent", Golos continues its work in Russia. "Even though things are getting tougher, we're still doing what we do," Andreichuk said.

Last year, Golos described the 2024 election that returned Putin for a fifth term with over 88% of the vote as the most fraudulent and corrupt in the country's history.

The Kremlin said the result showed that the Russian people had "consolidated" around Putin, and Western attempts to portray the election as illegitimate were absurd.

Andreichuk said the Melkonyants trial should matter to the outside world because Golos's work was part of a struggle for democracy.

"A real democracy in Russia wouldn't be a military threat. But an authoritarian government will keep threatening its neighbours," he said.

Rights group OVD-Info says more than 1,600 people are currently imprisoned in Russia on political grounds. The Kremlin says it does not comment on individual cases but that Russia needs to uphold its laws and protect itself against subversive activity.

(Reporting by Mark Trevelyan in London, Editing by Timothy Heritage)