A woman is shot outside a branch of Ukraine’s National Security Service in the western city of Khmelnytsky.
Graphic video posted on the internet showed a burst of automatic gunfire injuring several people as a crowd smashed the glass doors of the local headquarters of the SBU security service.
Raw footage of the shooting is too disturbing to be shown here but has been posted on YouTube and been viewed more than 100,000 times.
Onlookers screamed as a woman fell to the ground, bleeding heavily from what appeared to be a gunshot wound to the head.
Video footage showed a cluster of bullet holes appearing in a pane of glass next to the door, and pools of blood on the ground where the woman had been lying.
The woman was taken to hospital by ambulance. Some local media sources reported that she had died, while others said she was being treated in intensive care.
Another protester was filmed apparently bleeding from a bullet wound to the upper abdomen. Some Ukrainian news sites claimed a third protester had also been hit by bullets.
The location and identity of the shooter was not immediately obvious. Local media blamed the shooting on a security service “sniper”.
Local police said no one had died in the incident, and local media quoted named law enforcement officials as promising an investigation.
Despite the gunfire, the crowd of anti-government protesters did not disperse but carried on shouting slogans and pushing empty buses towards the entrance of the SBU building.
Local reports said the demonstrators had demanded a meeting with the head of the security service before they began to smash the doors.
The incident is one of the bloodiest outbreaks of violence to take place outside the capital, Kiev, where at least 26 people have been killed in fighting in recent days.
Ukraine’s health ministry said 10 of the dead were police officers, adding that a further 263 and 342 police officers have been treated for injuries, mainly gunshot wounds.
The European Commission president, Jose Manuel Barroso, spoke to Ukraine’s president, Viktor Yanukovych, by telephone on Wednesday to condemn the use of force against protesters and to call for an immediate end to violence.
The commission said in a statement: “He conveyed his shock and dismay with the recent clashes in Ukraine which led to an important number of dead and injured people.
“He called for an immediate end of the violence and firmly condemned the use of force to solve the political crisis.”
The EU and the US say they are discussing the possibility of economic sanctions against Ukraine in a bid to persuade Mr Yanukovych to reach a compromise with the protesters.