Updated

Russian election officials on Wednesday accused protest leader Alexei Navalny of using dirty tactics in his bid for Moscow mayor after police raided an apartment used by supporters and seized campaign materials.

Navalny is standing as an independent candidate in the elections on September 8 for Moscow mayor, a poll he wants to use as a springboard for a nationwide challenge to President Vladimir Putin.

Police said Wednesday that they raided a Moscow apartment after being tipped off that it contained illegal campaign materials and detained four people who were charged with resisting police.

Navalny was allowed to run for mayor in a surprise move after a court sentenced him to five years in prison last month for embezzlement in a disputed verdict. But he is facing intense scrutiny from the authorities.

Rossiya 24 television reported that a rival candidate for mayor, Nikolai Levychev of A Just Russia party, tipped off the police.

The channel showed police carrying out an activist by his arms and legs after cutting open the door with a blowtorch.

The apartment contained stickers and posters backing Navalny, Rossiya 24 reported, showing some with his official slogans on and some with different wording.

Navalny's campaign team said in a statement that those detained were from a group of supporters called Brothers of Navalny that was "acting fully independently" from the official campaign.

His team accused police of beating those detained.

A court later fined one of the activists 1,000 rubles ($30, 23 euros), the Interfax news agency reported.

The Moscow electoral commission on Wednesday accused Navalny of using corrupt practices and said it would take "necessary measures" depending on the result of an investigation by law enforcement authorities.

"It's disappointing that a candidate who positions himself as a 'fighter against corruption' himself uses 'dirty' technologies and shadowy schemes for his election campaign," the commission chief Valentin Gorbunov said in a statement on its website.

According to law, candidates have to put information on all their campaign materials about who produced them and with what print run.

Navalny's team said in a statement that all their campaign materials were "in strict accordance with electoral law".

Earlier this week prosecutors accused him of receiving illegal foreign funding via an online payment system.

The opposition leader's campaign fund is worth just under $1 million (755,000 euros), while the acting mayor Sergei Sobyanin has a fund worth more than $3 million.