MOSCOW (Reuters) - Kremlin critic Alexei Navalny is ineligible to run for the Russian presidency next year unless he can overturn a conviction for embezzlement, a senior election official was quoted as saying by Russia’s RIA news agency on Wednesday.

FILE PHOTO: Russian opposition leader Alexei Navalny attends a hearing after being detained at the protest against corruption and demanding the resignation of Prime Minister Dmitry Medvedev, at the Tverskoi court in Moscow, Russia March 27, 2017. REUTERS/Tatyana Makeyeva/File Photo

Navalny, who says he sees no legal impediment to his presidential run, organized the biggest anti-government protests in years in March, and has become the most prominent opposition challenger to President Vladimir Putin, who is expected to run for what would be a fourth presidential term in March 2018.

Navalny’s political plans were complicated in February when a court found him guilty of embezzlement at a retrial of a case which he said was politically-motivated and designed to sabotage his political career.

On Wednesday, a court rejected his appeal and upheld the original conviction which came with a five-year suspended prison sentence. Navalny’s legal team said it would now appeal to the European Court of Human Rights.

Allies say that Navalny, a 40-year-old lawyer turned opposition leader, is entitled to run for the presidency next year under the Russian constitution despite the embezzlement conviction.

The law is not explicit on whether he can run, leaving room for interpretation.

Nikolai Bulayev, deputy chairman of Russia’s Central Election Commission, told the RIA news agency on Wednesday that Navalny was currently ineligible to run and could only do so if he quashed his conviction via the courts.

“He (Navalny) is already trying to conduct a presidential campaign and, it seems to me, is manipulating people’s understanding about how the law, allegedly, does not apply,” said Bulayev.

“It’s a delusion. If he’s doing this deliberately he’s deluding other people. For now, as far as I understand, he does not have the right to stand for election and in order to get it he needs to act via the courts. There is no other way.”

Navalny says he has lost most of his sight in his right eye after an assailant threw green liquid in his face

If he is allowed to run and is up against Putin, who has not yet confirmed he will stand, opinion polls suggest Navalny will lose by a big margin.

Some analysts believe the Kremlin may ultimately allow Navalny to run in order to boost turnout and create the impression of some genuine political competition.

However, having Navalny on the ballot paper could be an irritant for the Kremlin by providing a focus for anti-Kremlin protests, especially in the big urban centers where Navalny draws most of his support.

Leonid Volkov, a Navalny ally, said on social media on Wednesday that he and fellow activists would fight for their leader’s right to run.

“Nobody promised it would be easy,” said Volkov. “Navalny has the right to run, but ensuring he is able to exercise it won’t be easy.”