US Secretary of State John Kerry warned yesterday that Russia was sending agents into eastern Ukraine to "create chaos" the Kremlin could use as a pretext for more military intervention.
Kerry's warning came as Ukraine's state security service said that pro-Russian separatists had placed explosives in a building they seized in the eastern city of Luhansk and were using weapons to hold about 60 people against their will. Pro-Russian separatists occupied the SBU building on Sunday evening in one of a series of attacks in the east of the country.
Kerry bluntly accused Russia of mounting an "illegal, illegitimate effort to destabilise a sovereign state".
"Everything that we've seen in the last 48 hours, from Russian provocateurs and agents operating in eastern Ukraine, tells us that they've been sent there determined to create chaos," Kerry told US lawmakers. He said Moscow was seeking to further destabilise neighbouring Ukraine by fomenting separatism.
"No one is fooled by what could potentially be a contrived pretext for military intervention just as we saw in Crimea."
Watch: Kharkiv government HQ target of cycle of violent protest
Ukrainian authorities earlier sent security forces to Kharkiv in the east to clear the city, the country's second-biggest, of separatists. Shots were fired, a grenade thrown and 70 people detained as officers ended the occupation of Kharkiv during an 18 minute "anti-terrorism" action, the interior ministry said.
Russia warned that the crackdown may spark a civil war.
Its foreign ministry also alleged that 150 specialists from the US private security company Greystone were working with Ukraine to put down protests.
The US had earlier thrown its weight behind Ukrainian officials' contention that some of the pro-Russian separatists who seized administration buildings in the cities of Luhansk and Donetsk were paid provocateurs brought in from outside.
"We do have proof and we've already deported a number of Russians who've been in eastern Ukraine provoking the situation and violating Ukrainian laws," Ukrainian Foreign Minister Andriy Deshchytsia said. "The Ukrainian government has enough power and authority to control the situation in Ukraine."
Deshchytsia said any suggestion that Greystone was playing a role in the crackdown was "just Russian propaganda, nothing else". In the Ukrainian parliament, deputies brawled after a communist leader accused nationalists of playing into Russia's hands by adopting extreme tactics early in the crisis.
Two deputies from the Svoboda far-right nationalist party took exception to the charges by communist Petro Symonenko and seized him while he was talking from the podium. His party supporters rallied to his defence and a fight broke out, with deputies from other parties joining in and trading punches.
Symonenko said nationalists had set a precedent earlier this year by seizing public buildings in protest at the rule of ousted president Viktor Yanukovych.
The demonstrations in the eastern cities have resembled the actions of pro-Russian protesters who seized Crimea's assembly and paved the way for Russia to annex the Black Sea province last month.
President Vladimir Putin, who has massed troops on Ukraine's border, says he has the right to defend Russian speakers from "fascists" after the Russian-backed Yanukovych's ousting.
Additional reporting by ReutersMore on this: