MOSCOW — Thousands of pro-Russian activists put Russian flags on top of seized administrative buildings in three major cities of Eastern Ukraine: Kharkiv, Donetsk and Lugansk on Sunday. And now the protestors have declared independence from what they call the “junta rulers” in Kiev, the capital.

As the demonstrators broke through rows of policemen, they chanted: “No to elections! Yes to a referendum!” calling for a Crimea-style vote that could lead to annexation by Russia. Once inside the administration building in Donetsk the occupiers proclaimed “a sovereign democratic state” and asked Russian President Vladimir Putin to bring military peacekeepers. Then they announced the date for their referendum as May 11, two weeks before Ukraine is due to hold national presidential elections.

Since early March, pro-Russian demonstrators have taken to the streets and clashed with police in normally peaceful Eastern Ukraine just about every weekend. The authorities are concerned that if they overreact, Putin will follow through on his promise “to defend Russian speakers,” and will roll his army across the border. So the Ukrainian government has tried to bring the situation under control without bloodshed. But this time the turmoil looks especially serious. During a police operation on Monday, authorities managed to push protesters out of the administration building in Kharkiv, but two protesters were injured seriously.

Using the same techniques and tactics as the pro-European protestors in the Maidan, who brought down the Kremlin-friendly government in Kiev in February, these pro-Russian activists barricaded themselves inside the occupied buildings with tires, broken furniture and barbed wire. At night, groups of pro-Russian militia, many in medical masks and with police shields in hand, stormed the regional headquarters in Donetsk and Lugansk of the Security Service of Ukraine, the domestic intelligence agency. They seized rooms with weapons in them and the archives of secret documents.

In spite of a growing number of arrests and investigations for separatism, angry activists continued to wave Russian flags and the “people’s republic” banners, which are banned by law, out of official buildings. Their actions, Ukraine’s prime minister Arseny Yatsenyuk said, are following “Russian-written scenarios aimed to dismember and destroy Ukraine.”

Nobody in Moscow denied there was a scenario. The anti-Kiev movement in Eastern Ukraine was “used as a tool for pushing Kiev to understand that Ukraine could never be free from Russia”, said Igor Bunin, director of the Center of Political Technologies, an independent think tank. But as long as there is no Russian blood spelled, no tanks would invade Ukraine, he said.

Russian flags on top of administration buildings have changed calculus, says Sergei Markov, the Kremlin’s expert on polls and political technology: “Russian authorities cannot ignore Russian flags.” Until now the Kremlin did not have plans to invade Ukraine, he said, because that would ruin relationships with the West, but Moscow’s priority was not to allow the supposedly “non-democratic” presidential elections in May.

If a referendum were held instead, according to Markov’s numbers, Kharkov would have 75 percent of its population voting to become a part of Russia; Donetsk, 80 percent; Odessa, 85 percent; Dnepropetrovsk, Zaporozhye and Kherson would have from 60 to 70 percent of pro-Russian votes. “There is still a big chance that the Kiev junta will kill people,” said Markov, “then the Russian army will have to defend the population.”

The government in Kiev urged law enforcement agencies to take actions to neutralize the protesters and prevent similar events in the future. “The country today has all the necessary power to quickly and adequately counter separatists and saboteurs,” wrote Yulia Tymoshenko, the former prime minister and current presidential candidate. “Any attempts by the Kremlin and its puppets to divide the country will not just be rejected but will also face strong opposition from Ukrainian society.”