* PM brands protesters "Nazis, extremists, criminals"
* Lavrov accuses some Europeans of hysteria
* Stand-off taking toll on fragile economy
* U.S.: Ukrainians must choose their future
By Matt Robinson
KIEV, Dec 6 Ukrainian pro-Europe demonstrators vowed to stay on the streets and continue their blockade of government buildings, despite a police threat to crack down "harshly" to enforce a court order that they disperse.
Kiev's Nov. 21 decision to abandon a trade and integration deal with the EU and pursue closer economic ties with Moscow brought hundreds of thousands of demonstrators into the streets over the weekend. Protesters have since blockaded the main government headquarters and occupied Kiev's city hall.
The government ratcheted up its rhetoric on Thursday, with Prime Minister Mykola Azarov branding opponents "Nazis and criminals." Kiev's police chief, Valery Mazan, threatened to "act decisively, harshly" if the protesters defy the court order to end their blockade and occupation of government buildings.
But the protesters showed no sign of retreating, with thousands remaining steadfastly camped out in the streets deep into the night.
"Let them come; we will stay," Igor Vorkuta, 47, said of the police. "This is a peaceful revolution, there are no guns here," he said, warming his hands on a brazier in the freezing winter cold near midnight in the square.
The crisis has exposed a gulf between Ukrainians, many from the West of the country, who hope to move rapidly into the European mainstream, and those mainly from the East who look to the former Soviet master Moscow as a guarantor of stability.
President Viktor Yanukovich had long promised to integrate with Europe while still maintaining friendly ties with Russia. His opponents, and some former supporters, considered his sudden eastward lurch a betrayal.
It has also reignited Cold War-era antagonism between Russia and Western Europe, even as foreign ministers gathered in Ukraine for a meeting of the Organization for Security and Cooperation in Europe, a body that includes both NATO members and the countries of the former Soviet Union.
European foreign ministers used their visits to Kiev to show open solidarity with the demonstrators, beginning with Germany's Guido Westerwelle who trekked to the square to meet opposition leaders on Wednesday. He was followed by others on Thursday.
Russia's Foreign Minister Sergei Lavrov, on the sidelines of the OSCE meeting, countered by accusing the Europeans of "hysteria".
Tension could be increased even further on Friday with new court proceedings against jailed opposition leader Yulia Tymoshenko. Brussels considers her a political prisoner and had campaigned in vain for her release before Kiev broke off negotiations.
SHARP WORDS FOR OPPOSITION
Azarov spoke sharply to Westerwelle on Thursday about the opposition, which includes far right nationalist groups as well as pro-European liberals.
"Nazis, extremists and criminals cannot be, in any way, our partners in 'Eurointegration'," the government website quoted Azarov as telling the German foreign minister.
Westerwelle expressed concern about police behaviour at the weekend's protests, when dozens of people were severely beaten.
"Recent events, in particular the violence against peaceful demonstrators last Saturday in Kiev worry me greatly," said Westerwelle. "The way Ukraine responds to the pro-European rallies is a yardstick for how seriously Ukraine takes the shared values of the OSCE."
EU countries, especially those like Germany and Poland with experience of Cold War-era Russian domination, are keen to bind Ukraine and its 46 million people closely with the West and say their trade pact would have brought a surge of investment.
Moscow, which has long opposed expansion of NATO or the EU to the territory of the ex-Soviet Union, wants Kiev instead to join a customs union it dominates. Russia exerts powerful leverage because of Ukraine's dependence on its natural gas.
The stand-off between pro-EU protesters and the government is taking a toll on the fragile economy. The central bank has twice been forced to support the currency this week and the cost of insuring Ukraine's debt against default has risen further.
Ukraine faces a $17 billion bill next year for debt repayments and deliveries of Russian gas. (Additional reporting by Pavel Polityuk and Natalia Zinets in Kiev, Megha Rajagopalan and Ben Blanchard in Beijing; Writing by Peter Graff; Editing by Cynthia Osterman)