KIEV, Ukraine — Security authorities in Ukraine offered the first indication Wednesday that the deadly political violence afflicting Kiev had spread far beyond the city limits, announcing a crackdown on what the Interior Ministry called “extremist groups” that had burned down buildings and seized weapons nationwide.

The Interior Ministry announcement of an “antiterrorist operation” across the country came a day after Kiev was gripped with the deadliest mayhem since protests erupted in November, leaving at least 25 dead, including nine police officers. The Health Ministry said that 241 people had been wounded.

The violence turned a protest encampment in Kiev’s central Independence Square into a fiery war zone and sharply escalated the political crisis that has convulsed the former Soviet republic of 46 million for the past three months. The crisis raised East-West tensions over Ukraine’s future, with Russia denouncing the protesters as Nazi-like coup plotters and the European Union threatening severe sanctions against Ukrainian government leaders. The United States said it might join the European sanctions effort.

President Viktor Yanukovych described the violence as an attempt to overthrow the government by his political adversaries, who want to push Ukraine closer to the European Union.

“Without any mandate from the people, illegally and in breach of the constitution of Ukraine, these politicians — if I may use that term — have resorted to pogroms, arson and murder to try to seize power,” the president said in a statement.

An announcement by the SBU, the Ukraine state security service, offered a new indication of turmoil extending 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, the head of the SBU, said in a statement.

“Courtrooms are being burned down, vandals are destroying private apartments, killing peaceful citizens,” the statement said. Yakimenko said the past 24 hours had shown “a growing escalation of violent confrontation and widespread use of weapons by extremist oriented groups.”<

In Kiev on Wednesday, protesters stoked what they called a “ring of fire” separating them from the riot police in a desperate effort to defend the remnants of a stage on Independence Square that has been a focal point of their protests.

Men staggering with exhaustion dismantled the tents and field kitchens from the protest movement’s earlier, more peaceful phase and hauled their remnants onto the fires. They piled on mattresses, sleeping bags, foam pads and whatever else looked flammable, burning their own encampment in a final act of defiance.

The Interior Ministry said all the police officers killed on Tuesday had died from gunshot wounds, although witnesses said it appeared that several officers had been trapped in a burning armored vehicle.
As the scope of the violence became clear, Russia — Yanukovych’s most important ally in the crisis — issued a blistering statement blaming the “criminal activities of radical opposition forces” for causing the bloodshed and denouncing European countries for refusing to acknowledge that. When the protests began late last year, demonstrators opposed the government’s rejection of a trade agreement with the European Union.

A statement Wednesday from the Russian Foreign Ministry described the violence as an attempted coup and even used the phrase “brown revolution,” an allusion to the Nazi rise to power in Germany in 1933.

The ministry said Russia would use “all our influence to restore peace and calm.”

A spokesman said President Vladimir Putin of Russia had spoken by telephone with Yanukovych and expressed support for a swift settlement, but said it was up to Ukraine’s government to resolve it without external interference.

“In the president’s view, all responsibility for what is happening in Ukraine rests with the extremists,” Dmitri S. Peskov, the spokesman, told reporters, according to the news agency Interfax.

On the other side of the barricades in Kiev, scores of exhausted riot police officers, their faces covered in soot, sat slumped on the sidewalk on Khreshchatyk Street, the main artery leading to Independence Square. Reinforcements poured in, massing in European Square, a large roundabout that sits astride main roads leading to the center of the city. One of these was clogged with around a dozen military-style dump trucks, armored cars and other vehicles.

But it was unclear whether the authorities had mustered sufficient force to complete the operation they began Tuesday to clear Independence Square. The security forces did, however, strengthen their grip on the Ukrainian House, a large modern building that had been occupied by protesters. Police officers carted out sacks filled with documents and garbage.

The Interior Ministry’s announcement of a nationwide crackdown came after witnesses and unofficial news reports from outside the capital said protesters had seized provincial administrative buildings in several regions, including Lviv, a bastion of anti-Yanukovych sentiment in western Ukraine near the border with Poland.

Andriy Porodko, a 29-year-old anti-government activist in Lviv, said by telephone that protesters had taken control of the central government’s main offices in the region, resuming an occupation that had ended last Sunday. He said they had also raided the local headquarters of the state prosecutor, the Ukrainian security service and several district police stations.

Most ominously, said Porodko, who last month organized a blockade of an Interior Ministry garrison on the outskirts of Lviv, around 1,000 protesters had stormed the garrison, which serves as the headquarters of the Interior Ministry’s western regional command, seizing control of barracks and weapons stores. A local journalist said that around 140 guns were seized from Lviv’s central police station.

In Kiev, the fires kept security forces and their vehicles away from the stage as police officers seemed unwilling to risk driving through the blazes. It was unclear how long the debris of the protesters’ tent camp could fuel the bonfires sufficiently to prevent an assault by security forces.

The flames from the barricades defended the entrances to the square where riot police officers were pressing forward but not streets leading from the plaza. Authorities appeared to be attempting to push the protesters out through those exits.

Protesters began pounding with clubs on utility poles and makeshift shields, creating a rhythmic din.

With the center of the city engulfed in thick, acrid smoke and filled with the deafening noise of grenades, fireworks and occasional gunfire, what began as a peaceful protest in late November against Yanukovych’s decision to spurn a trade deal with Europe and tilt toward Russia became on Tuesday a pyre of violent chaos.

The violence seemed likely to resonate for weeks, months or even years around this fragile and bitterly divided nation. It also exposed the impotence, in this dispute, of the United States and the European Union, which had engaged in a week of fruitless efforts to mediate a peaceful settlement.

Doubts about the influence of Russia were also shredded, as the Kremlin portrayed the protesters as U.S.-backed “terrorists” and, in thinly coded messages, urged Yanukovych to crack down.

U.S. Vice President Joe Biden telephoned Yanukovych to “express grave concern regarding the crisis on the streets” of Kiev and urged him “to pull back government forces and to exercise maximum restraint,” the vice president’s office said in a statement Tuesday.

U.S. Secretary of State John Kerry urged Yanukovych to stop the bloodshed. “We call on President Yanukovych and the Ukrainian government to de-escalate the situation immediately, and resume dialogue with the opposition on a peaceful path forward. Ukraine’s deep divisions will not be healed by spilling more innocent blood,” he said in a statement.

The German foreign minister, Frank-Walter Steinmeier, warned the Ukrainian government that it could face sanctions.
“Whoever is responsible for the decisions which have led to the bloodshed in Kiev and other parts of Ukraine should expect Europe to reconsider its position on imposing sanctions on individuals,” Steinmeier said in a statement Tuesday night. The bloodshed erupted only hours after Steinmeier had received the two main opposition leaders, Vitali Klitschko and Arseniy P. Yatsenyuk, in Berlin, where they also met Chancellor Angela Merkel.

The State Department, in an alert to U.S. citizens, said that travel into and out of the center of Kiev was restricted and described the situation as “currently very fluid.” It also warned that roving gangs had attacked journalists and protesters and committed other random acts of violence in Kiev and other cities.

“U.S. citizens whose residences or hotels are located in the vicinity of the protests are cautioned to leave those areas or prepare to remain indoors, possibly for several days, should clashes occur,” the notice said. “Further violent clashes between police and protesters in Kiev and other cities are possible. The location and nature of demonstrations and methods employed by the police can change quickly and without warning.”