Photos: Ukraine's Ring of Fire

Kiev's Independence Square became a fiery war zone Tuesday.

Ukrainian protesters take shelter behind metal shields.

Protesters at Kiev's Independence Square stand under metal shields to protect themselves against riot police armed with stun grenades and water cannon.

In bloody clashes Tuesday and Wednesday, 26 people—both government foes and supporters—were killed. (See also: "How History, Geography Explain Ukraine's Political Crisis.")

Ukrainian authorities said the military would begin an "anti-terrorist operation" to stop what it said was an attempt to overthrow the government of President Viktor Yanukovych.

The center of Kiev was engulfed Tuesday and Wednesday in the worst violence since the start of Ukraine's three-month political crisis.

Anti-government protesters create a makeshift catapult to use against police and Interior Ministry officials.

The Russian Foreign Ministry called the night of violence an attempted coup and used the phrase "Brown revolution," a reference to the rise of Nazi power in Germany.

Many protesters were wounded during the fighting in the square, but the violence spread to other quarters as well. A journalist with the daily Ukrainian newspaper Vesti, Vyacheslav Veremiy, was returning home at 2 a.m. when his taxi was besieged by a band of armed thugs. He was shot in the chest and died.

The protesters defended what was left of their encampment by creating a ring of fire fueled by the burning of tents, field kitchens, and other equipment.

The head of Ukrainian state security said Tuesday night's turmoil extended well beyond Kiev. "In many regions of the country, municipal buildings, offices of the Interior Ministry, state security and the prosecutor general, army units and arms depots are being seized," Oleksandr Yakimenko said in a statement.

A Ukrainian officer from the Berkut special forces appears ready to hurl a Molotov cocktail during the bloody protests in Kiev. President Yanukovych blames the violence on the "criminal activities of radical opposition forces," and criticized the West for its unwillingness to see the crisis in those terms.

Ukrainian riot police stand guard as they are bombarded by Molotov cocktails that spark a fire in their midst during violent clashes on Tuesday. Ukrainian President Yanukovych said there was no longer room for compromise now that the anti-government protesters had resorted to arms.

The opposition also stiffened its stance. "All the world is watching Ukraine," said opposition leader Vitali Klitschko, a former heavyweight boxing champion. "I can't imagine working with Yanukovych's government now."

Anti-government protesters hold a photo of Ukraine's President Yanukovych after ransacking the offices of the pro-presidential Party of the Regions in Kiev on Tuesday.

Several thousand anti-government protesters clashed with police near Ukraine's parliament, torching vehicles and hurling stones in the worst violence to rock Kiev, the capital, since the political crisis started three months ago.

A protester finds cover during pitched battles with police in the streets of Kiev on Tuesday.

The protesters accused President Yanukovych of ignoring their demands to enact constitutional reforms that would limit the president's powers. Parliamentarians loyal to the president were stalling on taking up the legislation that addressed the reform.

The outbreak of violence led to at least 250 injured and 26 dead. On Wednesday morning the protesters prepared for confrontation by pouring petrol into plastic bottles for fire bombs and crushing the pavement into pieces to build extensive barricades. The Ukrainian authorities sent riot police, special forces, and regular military into the streets.

Riot police use laser pointers to target anti-government protesters during clashes in the early morning hours of Wednesday in Kiev.

Prayers, rest, and first-aid are the principal activities in Mikhailovsky Zlatoverkhy church (St. Michael's), a golden-domed cathedral in the center of Kiev that provided sanctuary to anti-government demonstrators during a fresh outbreak of violence on Wednesday.

A man walks from the burning debris of Independence Square, known as the Maidan, after violent clashes that left the area around the square devastated.

After a night of violent struggle, the two sides were more divided than ever, with protesters vowing to fight to the end. The protests began late last year after the president rejected a trade agreement with the West and accepted a $15 billion bailout from Moscow.