KIEV, Ukraine –  More than 100,000 demonstrators chased away police to rally in the center of Ukraine's capital on Sunday, defying a government ban on protests on Independence Square, in the biggest show of anger over the president's refusal to sign an agreement with the European Union. Thousands of demonstrators tried to storm the nearby presidential administration building, but were driven back by riot police using tear gas and flash grenades, which produce a loud bang but are not intended to cause injury. The standoff continued, with more demonstrators arriving. The protest was led by prominent opposition politicians, who...