As Ukrainian authorities cracked down on pro-Russia protesters Tuesday after recent unrest that escalated over the weekend, Russia issued a warning against the use of force and also alleged that a private U.S. military contractor is assisting Ukraine.

From the LA Times:

Ukrainian riot police on Tuesday cleared a regional administration building and public square in the eastern city of Kharkiv of hundreds of pro-Russia protesters, detaining scores in the process, officials said.

“Seventy criminals were taken into custody during the operation,” Ukraine’s acting president, Oleksandr Turchynov, told the parliament in televised remarks Tuesday morning.

In response, Russia’s Foreign Ministry issued a stern warning against the use of force on pro-Russia protesters in eastern Ukraine and alleged the direct involvement of private U.S. military experts.

“According to our information, Ukraine Interior Ministry and National Guard troops including militants of the illegal armed group the Right Sector are being brought to the southeast regions of Ukraine,” read a statement posted on the Russian Foreign Ministry’s official website Tuesday. “A special concern is connected with the fact that about 150 U.S. experts from the private military organization Greystone dressed in the uniforms of [Ukraine] special unit Sokol are involved in the operation.”

“The organizers and participants in the operation are assuming huge responsibility for the creation of threats to rights, freedoms and lives of peaceful residents of Ukraine,” the statement said.

Further, Russia warned that use of force in the attempts to quell the unrest “could lead to civil war,” according to CNN.

In response to Russia’s accusations of the involvement of Greystone, a representative from the company told the Wall Street Journal, “We do not have anyone working in Ukraine nor do we have any plans to deploy anyone to the region.”

Meanwhile, just as on Monday, Washington DC again warned of potential additional sanctions against Russia should its forces move into eastern Ukraine.

From CNN:

Secretary of State John Kerry said Tuesday that Russian forces and special agents have been behind what he called the “chaos” in eastern Ukraine in the past 24 hours. Kerry described the developments as “more than deeply disturbing” and said they amounted to what could be a “contrived pretext for military intervention just as we saw in Crimea.”

He followed up by warning of increased sanctions targeting Russia’s banking, energy, mining and arms sectors if the Russians “cross over” into eastern Ukraine. Current sanctions target individuals over the Crimean annexation.

And in a testy exchange during a Senate committee hearing Tuesday, Arizona Senator John McCain criticized Kerry on a series of foreign policy matters, including Ukraine. Via the Washington Free Beacon:

“On the major issues, this administration is failing very badly. On the issue of Ukraine, my hero, Teddy Roosevelt, used to say, talk softly but carry a big stick. What you’re doing is talking strongly and carrying a very small stick — in fact, a twig,” McCain [said to Kerry].

Watch the rest of the exchange below.

[Featured image: April 7 Associated Press video via LA Times]