Alexi Navalny, a Russian opposition leader, was hospitalized on Sunday from an allergic reaction.

His hospitalization comes on the same weekend that hundreds of people were detained by Russian police in protests on Saturday over the decision to eliminate opposition-minded candidates from upcoming local elections.

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Russian opposition leader Alexei Navalny, currently serving a jail stint for calling for unauthorized protests, was hospitalized after suffering an acute allergic reaction on Sunday, his spokeswoman said.

Navalny was jailed for 30 days this week for calling for an unauthorized march to protest against the exclusion of several opposition-minded candidates from a local election later this year.

Police rounded up more than 1,000 people in the Russian capital at the march on Saturday in one of the biggest crackdowns of recent years against the opposition.

Read more: Russian police detained at least 500 political protestors calling for fair elections

Kira Yarmysh, Navalny's spokeswoman, wrote on Twitter that he had been hospitalized on Sunday morning with "severe swelling of the face and skin redness."

She said the cause of Navalny's allergic reaction was unknown and that he had never had suffered from such reactions in the past.

The Russian Interior Ministry and the Moscow hospital where Navalny's spokeswoman said he was being treated could not immediately be reached for comment.

Navalny, Russia's most prominent opposition figure, has served several stints in jail in recent years for organizing anti-government demonstrations.

The European Court of Human Rights last year ruled that Russia's arrests and detention of Navalny in 2012 and 2014 were politically-motivated and breached his human rights, a ruling Moscow called questionable.

(Reporting by Gabrielle Tétrault-Farber; Editing by Raissa Kasolowsky)