DONETSK, Ukraine (AP) — Pro-Russian activists barricaded inside a government building in eastern Ukraine proclaimed the region independent Monday and called for a referendum on seceding from Ukraine — an ominous echo of the events that led to Russia's annexation of Crimea.
The Ukrainian government accused Russia of stirring up the unrest and vowed to quell it. Russia, which has tens of thousands of troops massed along the border, warned Ukraine of more "difficulties and crises" if its leaders fail to heed Moscow's demands.
In Washington, the U.S. warned Russia that any move into eastern Ukraine would be a "very serious escalation" that could bring further sanctions. White House spokesman Jay Carney said there was strong evidence that some of the pro-Russian protesters in Ukraine were paid and were not local residents.
At the same time, the U.S. announced that Secretary of State John Kerry will meet with top diplomats from Russia, Ukraine and the European Union in a new push to ease tensions. The meeting will take place in the next 10 days, the State Department said.
Pro-Russian activists who seized the provincial administrative building in the city of Donetsk over the weekend announced the formation Monday of the independent Donetsk People's Republic.
They also called for a referendum on the secession of the Donetsk region, which borders Russia, to be held no later than May 11, according to the Interfax news agency.
Russia annexed Crimea last month, following a referendum called just two weeks after the Black Sea peninsula had been overtaken by Russian forces. Ukraine and the West have rejected the vote and the annexation as illegal.
Outside the Donetsk building, a barricade of car tires and razor wire was erected to prevent police from retaking it. Other armed activists fired warning shots and tried to seize the regional state television building in Donetsk but retreated Monday after police and guards in the building also fired in the air, Interfax cited police as saying.
Government buildings were also seized in two neighboring Russian-speaking Ukrainian cities — Kharkiv and Luhansk — and top government officials headed there to try to quell the unrest.
Authorities said the pro-Russian occupiers in all three cities were armed.
In Kiev, President Oleksandr Turchinov described the developments in eastern Ukraine as an operation undertaken by Russia to sow instability.
"Anti-terrorism measures will be adopted against those who took up weapons," Turchinov said, adding that Parliament would convene on Tuesday to consider tougher penalties for separatist actions and a ban on separatist parties.
Ukrainian Prime Minister Arseniy Yatsenyuk accused Russia of fomenting the unrest to create a pretext for sending troops across the border.
"The plan is to destabilize the situation. The plan is for foreign troops to cross the border and seize the country's territory, which we will not allow," he said, adding that those taking part in the unrest had distinct Russian accents.
Swedish Foreign Minister Carl Bildt also said the events in eastern Ukraine were part of Moscow's "destabilization strategy."
"Those who thought that it ended with Crimea were wrong," Bildt said.
The Russian Foreign Ministry rejected the Ukrainians' allegations but reaffirmed its long-held demand that Ukraine change its constitution to turn the country into a federation with broader powers for provinces. It such move should also underline Ukraine's non-aligned stance and ensure a special status for the Russian language.
"If the political forces that call themselves the Ukrainian government continue to take an irresponsible attitude to the fate of the country and its people, Ukraine will inevitably face new difficulties and crises," the ministry said in a statement.
Eastern Ukraine, which has a large population of ethnic Russians, was the base of support for ousted President Viktor Yanukovych, who fled to Russia in February after months of protests. Economic and cultural ties to Russia are strong here, and many are wary of the new government, which favors closer ties to the European Union.
But Ukraine's interim authorities deny they are infringing on the rights of ethnic Russians or Russian-speakers, and there has been no evidence they are being harassed.
NATO says up to 40,000 Russian troops have mobilized along the Ukrainian border and present a distinct threat to Ukraine. Russia says it has the right to move its troops wherever it wants on its own territory.
In a video posted on the Internet, an unidentified pro-Russian activist in the Donetsk government headquarters asked Russian President Vladimir Putin to send peacekeeping troops into the region.
"Without your support, without the support of Russia, it will be hard for us to resist the Kiev junta on our own," the man said, referring to the interim authorities that took power in Ukraine after the overthrow of Yanukovych.
But a senior Russian lawmaker suggested Monday that such a move was not imminent. Viktor Oserov, head of the defense committee in the Russian Parliament's upper house, said Moscow cannot send peacekeepers in without a U.N. Security Council resolution, according to Interfax.
The ITAR-Tass state news agency cited the deputy speaker of Russia's upper house of Parliament, Ilyas Umakhanov, as saying of the unrest in Donetsk: "I don't think this situation automatically reflects what happened in Crimea."
Russian news agencies also reported Monday that prosecutors have opened a criminal investigation into the death of a Crimea-based Ukrainian army major who was shot by a Russian soldier in a scuffle Sunday.
Jim Heintz and Vladimir Isachenkov in Moscow, Karl Ritter in Stockholm and Maria Danilova in Kiev contributed to this report.