Foreign diplomats have converged on a tense Ukrainian capital, which is gripped by massive protests against the government's decision to freeze ties with the EU and turn to Moscow instead.

Several thousand activists continued rallying on a central square and besieging government meetings early Thursday as delegates from Western states joined a meeting of Europe's top security body.

With President Viktor Yanukovych away in China, the government showed no sign of yielding to protests. Police have promised not to use force, but law enforcement bodies were detaining and investigating scores of opposition activists.

The demonstrators were sparked by Yanukovych's decision ditch a significant treaty with the European Union after strong pressure from Russia. They were also galvanized by a violent break-up of a small, peaceful rally last month.