The US today called on Russian President Vladimir Putin to stop "destabilising" Ukraine, expressing concern over several escalatory moves over the weekend.

Attributing the recent moves primarily to the recent Russian annexation of Crimea, the US warned Russia against intervening in eastern Ukraine and threatened further sanctions, this time targeting the Russian economy if the situation continued to escalate.

"If Russia moves into Eastern Ukraine, either overtly or covertly, this would be a very serious escalation. We call on President Putin and his government to cease all efforts to destabilise Ukraine, and we caution against further military intervention," White House Press Secretary Jay Carney said.

"We're concerned about several escalatory moves in Ukraine over the weekend, and we see those as a result of increased Russian pressure on Ukraine," Carney told reporters.

"We saw groups of pro-Russian demonstrators takeover government buildings in the Eastern cities of Kharkiv, Donetsk and Luhansk, and there is strong evidence suggesting some of these demonstrators were paid and were not local residents."



In Donetsk, a handful of pro-Russian separatists in the barricades Donetsk Oblast government administration, declared the creation of the Donetsk People's Republic, announced a so-called referendum on May 11th, seeking to join Russia, and requested Russia send in military peacekeepers, Carney said, adding these people lack the legal authority to make any of those decisions.

According to the White House, there is strong evidence that some demonstrators were paid and that they were not local residents.

"I think that at least suggests that outside forces, not local forces, were participating on the effort to create these provocations.

"What's clear is that this is a result of increased Russian pressure on Ukraine. And we see it in the troops that have massed on the border. We see it in a variety of developments internally within Ukraine, in the regions of the country where there are more ethnic Russians, in some of the concerns expressed about the fate of ethnic Russians," Carney alleged.