The streets of Kiev were plastered with images of a young woman's bruised and swollen face on Thursday morning. The almost unrecognisable photograph was of Tetyana Chernovil, a journalist known for her investigations into government corruption, who has been in intensive care preparing for a series of operations to repair her face, shattered in a beating by unknown assailants.

Hundreds of protesters gathered outside the interior ministry headquarters, accusing authorities of ordering police officers to carry out the attack.

"It is a shame to beat women on the head," the crowd chanted. "Zakharchenko is an executor. He should resign," others cried, referring to the interior minister, Vitaly Zakharchenko – reviled by the opposition activists who for the past month have led hundreds thousands of Ukrainians in protest against the Russian-allied government.

Chernovil, 34, has been badly disfigured by the assault . Her colleagues at the Ukrainskaya Pravda newspaper recount Chernovil's description of how her attackers chased her before beating her up in the early hours of Wednesday morning.

Chernovil told police she was driving home when she noticed she was being followed by a dark SUV, which then forced her off the road. Several men jumped out and smashed her rear window, dragged her from the car, beat her and abandoned her in a ditch, a police statement said.

"It is scary and very sad to see what they have done to Tetyana," Chernovil's friend and colleague Maria Lebedeva told the Guardian.

Chernovil was known for her investigations and protests against alleged corruption among senior state officials, including Zakharchenko.

From the hospital bed where doctors are treating her for concussion, fractured facial bones, a severely broken nose and bruising, Chernovil told friends that on the day of the attack, she had written about Zakharchenko's luxurious estate, which she said was unaffordable on a government salary.

Chernovil – who is as much an activist as a journalist – has also led investigations into police brutality.

Lebedeva described how, earlier this month, she had photographed Chernovil leading a group of activists to Zakharchenko's apartment building carrying a stuffed figure of a policeman bearing the word "executor".

"The activists put that policeman into a garbage bag – the idea was to say, if the minister does not resign, people will think of all policemen as garbage," Lebedeva said.

General Vitaly Yarema – a former Kiev police chief who has joined the opposition protests – told local media that Chernovil had "suffered for her social activism".

Yarema is leading an independent investigation into her attack from the opposition headquarters on Independence Square, Kiev (known as the maidan) focal point for the anti-government protest movement. He is studying video footage captured by a camera in Chernovil's car, which her supporters say shows the three attackers and the licence plate of the car they were driving.

"I believe we will quickly find out the truth with the help of General Vitaly Yarema, a professional criminal investigator on this case," an opposition parliament deputy, Anatoly Gritsenko, said in an interview.

Hundreds of reporters took to Kiev's streets to protest on Thursday and vowed to continue the investigations Chernovil had started. By the afternoon, a cavalcade of 15 cars and a bus full of journalists had set off for Zakharchenko's summer cottage.

"They call it the Mobile Maidan. In spite of violence used against protesters, reporters and activists are determined to go right to the minister's windows to support their colleague," said Mari Bastashevski, a researcher and artist.

After more than a month of pro-EU protests in the central square of Kiev, Chernovil's case has rapidly become a symbol for the Ukrainian opposition and a totem around which Ukraine's journalists – hampered by routine violence and rights abuses – are rallying.