MOSCOW (Reuters) - Russian opposition figure and anti-graft campaigner Alexei Navalny announced on Tuesday he plans to run for president in 2018, causing a potential headache for the Kremlin.

Russian anti-corruption campaigner and opposition figure Alexei Navalny attends a hearing at the Lublinsky district court in Moscow, Russia, August 1, 2016. REUTERS/Maxim Shemetov

Navalny is very unlikely to pose a serious threat to President Vladimir Putin, who will be overwhelming favorite to win re-election if, as expected, he decides to seek another term.

But his candidacy would force the Kremlin to either exclude him from the race, leaving it open to allegations that the election is unfair, or risk the embarassment of Navalny picking up a large protest vote, said political analyst Yekaterina Schulmann.

“There have not been competitive elections in Russia for 20 years,” Navalny, 40, the founder of Russia’s Anti-Corruption Foundation, said in his statement.

“I’m sick and tired of watching ‘elections’ with the candidates just making up the numbers, not daring to criticize the pre-determined winner. I understand very well that for me even to become a candidate would not be easy.”

Navalny has accused top government officials from Putin’s inner circle of taking bribes and kick-backs and of stealing government funds.

Since 2011, he has faced several criminal cases against him with one leading to a suspended five-year sentence.

A court in Russia’s Kirov region found Navalny and an associate guilty of embezzling funds from a timber firm and in 2013 sentenced him to five years in jail, a sentence that was later suspended on appeal. Navalny has long said all charges against him were politically motivated.

Last month, Russia’s Supreme Court struck down the suspended year sentence..

“(After that decision) Navalny is free to take part in elections”, his lawyer, Olga Mikhailova, told Reuters.

Russian law bans anyone convicted of a serious crime of running in elections. Someone can apply to be a candidate in a presidential vote if they collect 300,000 signatures.

Navalny enjoys some popularity among the urban middle classes, especially in Moscow and St Petersburg.

He ran for mayor of Moscow in 2013, and though he lost to a Kremlin-backed candidate, he took second place with 27.24 percent of votes cast.

But Navalny has struggled to widen his appeal. State-run television, primary source of news for most Russians, usually shows him in a negative light.