Russian opposition leader Aleksei Navalny and his supporters have accused a notorious Russian nationalist group of assaulting him with a green antiseptic -- known in Russian as "zelyonka" -- in an attack that could leave him with permanent eye damage.
One member of the group, which calls itself the South East Radical Block (SERB), admitted to the respected independent Novaya Gazeta newspaper that he filmed the April 27 attack in Moscow, a disclosure that came after a Navalny supporter uncovered hidden videos on a Russian TV network's website showing the man, Aleksei Kulakov, at the scene.
But both he and SERB leader Igor Beketov, an actor who goes by the nom de guerre Gosha Tarasevich, have denied that the group was involved. Beketov said in a radio interview that the activist accused by Navalny of carrying out the assault, a man named Aleksandr Petrunko, has an alibi clearing him of complicity in the attack.
Navalny, who has accused authorities of failing to investigate the incident, said his doctor believes that the zelyonka -- a common weapon used in attacks against opposition activists -- was mixed with another substance that caused chemical burns to his right eye.
WATCH: Zelyonka -- The Green 'Weapon Of Choice'
The incident has cast a national spotlight on SERB, which by its own account consists of just a handful of "radical" members whose goal is to "support a cult of traditional Russian family values and put an end to the moral decay of society being forced upon us by the West and America."
To this end, it says it reserves the right to use any method in line with its "conscience," which appears to include dousing political opponents not only with zelyonka but also human waste.
Here's a look at SERB and its harassment of Kremlin critics and others it deems insufficiently patriotic.
SERB appears to have emerged in eastern Ukraine around the time of the 2014 ouster of President Viktor Yanukovych, a Kremlin ally, amid mass street protests that preceded Russia's annexation of Ukraine's Crimean Peninsula and backing of armed separatists in eastern Ukraine.
Beketov's acting profile states that he graduated from university in the eastern Ukrainian city of Dnipropetrovsk, and both he and Petrunko claim they took part in 2014 protests in another eastern city, Kharkiv, against the pro-Western government that took power in Kyiv after Yanukovych fled to Russia.
Petrunko claimed in an interview last year that he was arrested by Ukrainian security services after he participated in an unsuccessful bid to seize a government building in Kharkiv, the Russian website Znak.com reported. Sometime after that, both he and Beketov made their way to Russia, where they subsequently began staging guerrilla actions against Kyiv supporters and Kremlin opponents. Many of these stunts have turned violent.
Let Them Eat Cake … And Feces
While SERB has denied splashing zelyonka on Navalny, the assault was consistent with the style of the group. Its activists have used a range of substances in its attacks on opponents, including fecal matter and urine.
In February 2015, SERB members scuffled with activists from the Russian opposition group Solidarity who were staging a protest in central Moscow against the war between Ukrainian forces and Russia-backed separatists. At one point, an unidentified assailant tossed a plastic bag filled with feces at a Solidarity activist, smearing the target's coat with excrement.
Beketov took credit for the stunt in a subsequent Facebook post, saying the Solidarity protesters had "a liter of crap" dumped on them for "insulting" Russia and President Vladimir Putin.
SERB was suspected in an August 2016 attack against Russian journalist Yulia Latynina, a fierce Putin critic, in which an unidentified assailant tossed fecal matter from a bucket on her as she was walking on the street:
The group does not appear to have expressly claimed credit for that attack, though it has not denied involvement either. An interviewer sympathetic to SERB stated as fact in a February discussion with Beketov that the group had doused Latynina with feces. Beketov did not contradict the claim in the interview published by the website KolokolRussia.ru.
SERB published a gleeful post about the Latynina attack on its page on the Russian social-networking site VKontakte, winking at readers by saying that "there is every reason to believe" the group knows the circumstances behind the assault.
Petrunko, whom Navalny accused of attacking him with zelyonka, also served a short stint in jail last year after throwing urine at photographs by U.S. photographer Jock Sturges being exhibited at a Moscow museum. Petrunko denounced the images as child pornography.
SERB activists also doused an elderly anti-Kremlin protester with an unidentified green liquid in October 2015, saying they "defended the honor of the president and did not allow a group of traitors to Russia to insult our president."
Just over a year ago, meanwhile, a SERB activist smashed a cake into Navalny's face at the same place that the Kremlin opponent was doused with zelyonka last week: outside the Moscow office of his anticorruption group.
SERB activists have also attacked the makeshift memorial to the late Russian opposition politician Boris Nemtsov at the site of his February 2014 assassination on a bridge just steps from the Kremlin. The group, which calls Nemtsov a "traitor," has destroyed signs, photographs, and flowers placed there by the slain Kremlin critic's supporters in his honor.
"SERB fights and will always fight with traitors of Russia," Beketov wrote in a post about the destruction of the memorial, accusing Nemtsov of "always supporting America's interests and spitting on Russia's interests."
Kremlin opponents accuse Russian state media of conducting a demonization campaign against Nemtsov using similar rhetoric that they say helped lead to his killing, which several defendants from the Russian North Caucasus region of Chechnya are accused of carrying out.
Navalny has accused Putin's administration and Russian security services of involvement in the guerrilla attacks against him, including the most recent zelyonka attack. The Kremlin has previously denied being part of any campaign to discredit or intimidate Navalny, and Gazeta.ru on April 30 cited Kremlin "sources" as saying that it had no role in a spate of recent attacks against opposition activists.
No clear evidence has emerged suggesting the Kremlin is funding or otherwise directing SERB activists, though they have been able to get face time with senior Russian officials. Photographs have surfaced in recent days showing the group's members standing next to federal lawmakers and a senior Putin aide.
The photographs include one of Petrunko together with Pyotr Tolstoy, a member of Putin's ruling United Russia party and deputy speaker in the State Duma, Russia's lower house of parliament.
Another photograph shows Petrunko together with Kremlin economic adviser Sergei Glazyev, who has been sanctioned by both the United States and the European Union over Russia's seizure of Crimea.
In a blog post published one day before last week's attack on Navalny, Beketov posted photographs of himself inside the Duma and claimed he was invited there by federal lawmakers.
He claimed that he met with senior lawmakers who "listened very carefully" about SERB's experience in "resisting attempts to organize a Maidan in Russia," referring to the Kyiv square at the center of the protests that led to Yanukovych's 2014 ouster in Ukraine.
Yevgeny Revenko, a senior United Russia lawmaker in the Duma, wrote in a May 1 Facebook post that zelyonka attacks and other "hooligan" acts "are not a means of political battle, but rather a crime."
"I am certain that my party colleagues share this view," he wrote.
With reporting by RFE/RL's Russian Service