Viktor Yanukovich, Ukraine’s president, was under escalating pressure last night as hundreds of thousands of protesters poured on to the streets of Kiev demanding the overthrow of his government, after it sought to strengthen relations with Russia at the expense of the EU.

With the number of protesters estimated at some 350,000, the demonstrations mark the largest public gatherings since the 2004 pro-democracy Orange Revolution. Many called for a new “revolution” to end the president’s “bandit regime”.

Most people venting their anger against the government were peaceful but eyewitnesses reported that a large group of protesters had tried to use a tractor to break through police lines around the presidential building. Security forces responded with tear gas and flash grenades. Another group broke into the Kiev mayor’s office, Ukrainian television reported.