A top aide to Russian opposition leader Aleksei Navalny says he was attacked on the street with a metal pipe in Moscow, the latest incident in what Navalny calls a state-sanctioned campaign of violence and intimidation against supporters of his presidential bid.
Nikolai Lyaskin, head of the Moscow bureau of Navalny's presidential campaign, said on Twitter that shortly after he left the campaign headquarters in the city's central district on September 15, an unidentified assailant struck him several times from behind with the pipe and then fled the scene.
"Some scumbag just attacked me from behind," Lyaskin wrote.
Lyaskin said in a subsequent tweet that he was taken to the hospital by ambulance.
He told Russian media outlets that he was hit once in the back of the head with the pipe, but that the other blows largely missed their mark.
The extent of his injuries was not immediately clear.
Lyaskin posted photographs of what he said was the weapon, which was wrapped in newspaper. He told the RBK business daily that the weapon was a "steel pipe."
Lyaskin said later on September 15 that he was diagnosed with a concussion and posted a copy of the medical report on Twitter. He added that he was filing a police report.
The state-run TASS news agency quoted Moscow police as saying they were conducting a probe of the alleged attack.
Navalny and his supporters accuse the authorities of giving tacit approval to acts of violence against them by failing to identify and prosecute assailants targeting them.
"The attack on Nikolai Lyaskin is, of course, the result of the lack of police action against the scum who carried out earlier attacks," Ivan Zhdanov, a lawyer for Navalny, wrote on Twitter.
Navalny posted a photograph of the alleged weapon on Twitter, writing, "What is this if not attempted murder?"
Navalny himself suffered a chemical burn to his eye in April when an assailant splashed green antiseptic on the opposition leader's face. He underwent surgery in Spain the following month due to the injury.
The anticorruption crusader is attempting to run in the March 2018 presidential election, which is widely expected to hand President Vladimir Putin a new six-year term.
Since announcing his candidacy in December 2016, Navalny has opened more than 60 campaign offices in different regions of Russia.
In June, however, the Central Election Commission said that Navalny was ineligible to run for public office because of a financial-crimes conviction that he calls politically motivated.
The New York-based Human Rights Watch (HRW) said in a statement last week that "radical nationalists and pro-Putin groups have physically attacked and threatened" Navalny's campaigners, and that "official investigations into these incidents have not been effective."
HRW added that Russian police are "systematically" interfering with Navalny's attempts to run for president by raiding his campaign offices, "arbitrarily" detaining campaign volunteers, and carrying out "other actions that unjustifiably interfere with campaigning."
Putin has not announced whether he will run, but is expected to seek and secure a fourth term.
The Kremlin has dismissed Navalny, who finished second in Moscow's 2013 mayoral election with around 27 percent of the vote, as a convict and a marginal political figure.