A protest by about 300,000 Ukrainians angered by their government's decision to freeze integration with the West turned violent late yesterday, when a group of demonstrators besieged President Viktor Yanukovych's office in Kiev and police drove them back with truncheons, tear gas, and flash grenades. Dozens of people with what appeared to be head injuries were taken away by ambulance. Several journalists, including some beaten by police, were injured in the protests. Opposition leaders denounced the clashes as a provocation aimed at discrediting the peaceful demonstration and said that the people who incited the storming of the presidential office were government-hired thugs. (More Ukraine stories.)