SLOVYANSK, Ukraine Amid fresh warnings from Russian President Vladimir Putin, pro-Russian separatist leaders of the Donetsk People's Republic announced a mobilization of its forces in eastern Ukraine on Thursday in response to an anti-terror operation by Ukrainian authorities that has left five militants dead, Interfax Ukraine reports.

Ukraine's Interior Ministry said on its website that the militants were killed at a checkpoint in Slovyansk, which is held by forces loyal to Kiev. The Interior Ministry described the dead as terrorists.

A spokeswoman for the Slovyansk insurgents, Stella Khorosheva, told the Associated Press said she could confirm only that at least two pro-Russia fighters were killed during clashes.

The Interior Ministry has distributed leaflets in the city advising the local population to stay calm and not carry out the orders issued by self-proclaimed separatist authorities.

According to the ministry, the city's self-proclaimed mayor and local separatist leader, Vyacheslav Ponomaryov, has said those seen with the leaflet will be shot.

The push back by Ukraine's government against separatist strongholds in the Donetsk region comes in response to pro-Russia protesters and masked gunmen seizing government buildings and setting up checkpoints along roads 100 miles from the border with Russia.

Ukraine's State Security Service claimed Thursday it had recordings of phone conversations between separatists linking Ihor Strelkov, a Russian special forces officer, who is wanted in Ukraine for allegedly leading the separatist riots in the east, to the murder of Volodymyr Rybak, a city council deputy found dead near Slovyansk on Saturday.

The new standoff has emerged despite an agreement signed last week between Russia and Ukraine to ease tensions in the region.

Meanwhile, Russia's Defense Minister Sergey Shoigu has ordered several military units to start military exercises near Ukraine's border, according to Russia Today.

Putin's latest warnings, carried by Interfax, were delivered on Russian TV.

If the Kiev government is using the army against its own people this is clearly a grave crime, Putin said. He noted that recent events in eastern Ukraine proved that Russia's decision to annex the Ukrainian region of Crimea was the correct one.

At a secessionist checkpoint on the road to Slovyansk on Thursday, 60-year-old Alexander Malinovsky was helping check cars on the main artery. Dressed in faded camouflage fatigues but carrying no weapon, he said the people here want peace and protection from Kiev which they accuse of aggression.

We're not terrorists, he said. We just want to live on our own land.

At a former livestock feed plant, members of a heavily armed militia manned a smoking barricade they said was attacked by Ukrainian forces earlier Thursday. Holding up a glossy photo of a dark-haired youth, Ponomaryov, the self-proclaimed people's mayor of Slovyansk, said the man had been killed and another wounded.

Now get away from here, Ponomaryov warned reporters before hopping into a sedan with body guards. You're disturbing us.

Some in the east said the Kiev government's reaction to the protests in the area that is heavily populated by ethnic Russians was hypocritical.

I think this operation (by the Ukrainian army) is bad for civilians, said Tetiana Liubashenko, 21, who lives in Konstantinovka, a small city in the Donetsk region about 30 miles from Slovyansk, where Ukrainian police forces attacked pro-Russian protesters.

When Kiev had its EuroMaidan protest, people from the east didn't go there to stop it, said Liubashenko, a student at a university in Slovyansk. Now it looks like the rest of Ukraine can have democracy and freedom to decide its future like they did at Maidan but the east can't. It's wrong. I want to live in united Ukraine, but I think the east must be allowed to hold a referendum.

She was referring to protests in Kiev that ousted the pro-Russian government of Ukrainian president Viktor Yanukovych in February.

For some like Liubashenko the possibility of intervention by Russian troops is not a bad prospect.

It won't do any good for anyone, Liubashenko said. But out of the possible bad scenarios, this may be the best one.

Speaking from Japan on Thursday, President Obama accused Moscow of failing to abide by the spirit or the letter of the agreement. He also warned Moscow that the U.S. has more economic sanctions teed up.

I understand that additional sanctions may not change Putin's calculus, Obama said during a news conference in Tokyo with Prime Minister Shinzo Abe. How well they change his calculus in part depends on not only us applying sanctions but also the cooperation of other countries.

Olga Rudenko reported from Kiev. Contributing: Kim Hjelmgaard

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