18 people have been killed in violence in Ukraine overnight as police and protesters clashed.

Ukrainian riot police charged protesters occupying a central Kiev square early this morning, Wednesday, February 19, after the bloodiest day since the former Soviet republic, caught in a geopolitical struggle between Russia and the West, won its independence.

Police battled their way into Independence Square - centre of three months of protests against President Viktor Yanukovich - but demonstrators, some armed with clubs and wearing helmets and body armour, tried to stand their ground.

At least 18 people, including seven policemen, died on Tuesday during hours of violence between security forces and civilians. Many were killed by gunshot and hundreds more injured, with dozens of them in a serious condition, police and opposition representatives said.

Alarmed Western governments demanded restraint and dialogue. U.S. Vice President Joe Biden called Yanukovich, urging him to pull back the government forces and to exercise maximum restraint, the White House said.

Earlier, the state security service set a deadline for the demonstrators to end disorder or face “tough measures”. Then the police advanced up to the square before launching a full assault in the early hours, throwing stun grenades.

Nationwide demonstrations erupted in November after Yanukovich bowed to Russian pressure and pulled out of a planned far-reaching trade agreement with the European Union, deciding instead to accept a Kremlin bailout for the heavily indebted economy.