Despite Russia's veiled threat that any ongoing action against pro-Russian demonstrators had the potential to instigate civil war and bring action by the Russian forces, Ukraine's interior minister Arsen Avakov has announced, Reuters reports, that Ukraine has launched an "anti-terrorist" operation in the eastern city of Kharkiv and about 70 "separatists" have been arrested for seizing the regional administration building. Is this the red-line that Putin laid down last night?

As Russia made clear last night, as ITAR-TASS reports,

The Russian Foreign Ministry urged Ukraine to halt any interior military preparations, which could instigate a civil war in the country, the ministry was quoted as saying on its Facebook.com account. “According to our information, units of the Interior troops and Ukraine’s national guards as well as militants from the illegal armed formation ‘The Right Sector’ are being amassed in the southeastern parts of Ukraine and in the city of Donetsk,” the ministry said. “We are particularly concerned that the operation involves some 150 American mercenaries from a private company Greystone Ltd., dressed in the uniform of the [Ukrainian] special task police unit Sokol,” the ministry said.

But, in the interests of stability, as Ukraine also made clear yesterday, Reuters reports that

Ukraine has launched an "anti-terrorist" operation in the eastern city of Kharkiv and about 70 "separatists" have been arrested for seizing the regional administration building, Ukrainian Interior Minister Arsen Avakov said on Tuesday. On his Facebook page, Avakov said: "An anti-terrorist operation has been launched. The city center is blocked along with metro stations. Do not worry. Once we finish, we will open them again." Ukraine's Interior Ministry was quoted as saying by Interfax-Ukraine news agency that those detained were suspected of "illegal activity related to separatism, the organization of mass disorder, damage to human health" and breaking other laws.

So, it is clear that Ukraine's crackdown - with US mercenaries or not - has begun. The question is how long will Putin stand for it?