Ukrainian riot police have taken positions across the capital, Kyiv, as pro-Europe demonstrators continued their demonstrations against the government of President Viktor Yanukovych.
The policemen, wearing helmets and carrying shields, moved in a line near the city's Independence Square and a key administration building.
Protesters who have blocked access to the government building are facing a court-ordered to disperse or face ejection.
Ukrainian opposition leader Vitaliy Klitschko on Monday called on police to restrain from using force, describing the situation as being 'stretched like a string" and capable of switching toward either side.
"We are calling upon the law enforcement to restrain from using force against peaceful demonstrators. The result of this can be upsetting, not just regarding the beating of protesters, but resulting disturbance within all of society."
Opposition leader Arseniy Yatsenyuk said he hoped police would allow food and emergency services to get through to protesters camped in Independence Square.
"Right now the police major promised to open a corridor. If not, it will be bad".
The European Union has called for the Ukrainian government to show restraint, saying Europe has "the right and the duty" to support protesters.
The deployment of riot police came as Mr. Yanukovych agreed to talks with three former Ukrainian presidents in an effort to defuse the crisis over his refusal to sign a long-anticipated EU trade deal in favor of closer ties to Russia.
Russia has exerted strong economic pressure on cash-strapped Kyiv to discourage the EU deal. Russia is Ukraine's largest foreign investor, trading partner and chief natural gas supplier.
Moscow is seeking to form a trade bloc of former Soviet republics and satellite countries. Earlier this year, it imposed restrictions on goods from Ukraine, cutting Ukrainian exports 25 percent and dragging the country into recession.