Riot police encircled central Kiev on Monday night, raising fears the authorities were preparing a crackdown on anti-government protesters just hours after Ukraine's president said he was prepared to hold talks with opposition leaders.
The ominous police build-up came as the EU's foreign policy chief Catherine Ashton was preparing to fly into Kiev on Tuesday for talks with president Viktor Yanukovich.
Vitali Klitschko the heavyweight boxer-turned-opposition leader, warned that any move to clear protesters from the streets would be a sign that Mr Yanukovich was setting up a "police state".
Hundreds of riot police appeared to have surrounded the whole of the city centre, though they remained a short distance away from Independence Square, epicentre of the protests where thousands of demonstrators have camped out.
But three metro stations around the square were closed, and shopping malls above and below the square closed down operations early for the first time since protests began 19 days ago.
(Read more: Ukraine, Russia deny reports of deal)
Elsewhere in the city, masked men with machine guns late on Monday raided the headquarters of the Fatherland party of jailed opposition leader Yulia Tymoshenko, taking away computer servers, with one person present calling the scene "insane". Some opposition party and independent newspaper websites were also blocked.
Busloads of riot police were beginning to tear down barricades set up by protesters near government buildings in the capital, and were reported to have surrounded a group of demonstrators outside the presidential administration building.