Ukrainian police scuffled on Wednesday with supporters of former president Petro Poroshenko, who was due to appear in court in a treason case that he says was cooked up by allies of his successor, President Volodymyr Zelenskiy.
Critics say the case is an ill-judged distraction at a time when Ukraine is bracing for a possible military offensive by Russia, which visiting U.S. Secretary of State Antony Blinken said could happen at "very short notice".
Poroshenko, 56, is being investigated for treason linked to the financing of Russian-backed separatist fighters through illegal coal sales in 2014-15.
He faces up to 15 years in prison if found guilty, and his party accused Zelenskiy of a reckless attempt to silence political opposition.
Zelenskiy's administration says the prosecutors and judiciary are independent and accuses Poroshenko of putting himself above the law.
Zelenskiy trounced Poroshenko in an election in 2019, running on a ticket of tackling corruption and curbing the influence of oligarchs in the former Soviet republic.
Blinken appealed to Ukrainian leaders to present a united front against Russia.
"I think one of Moscow's long-standing goals has been to try to sow divisions, between and within countries, and quite simply we cannot and will not let them do that," he said while meeting Zelenskiy.
"So our message to all of our friends here, to all of Ukraine's political leaders, to its citizens alike, is to stick together and to hold on to that unity, to strengthen it. It's never been more important, particularly as the country faces the possibility of renewed Russian aggression."
Poroshenko's supporters said police had tried to remove tents where people were giving out tea and sandwiches.
"They want to take away everything that is in the tents, they are pushing us out. They surrounded us. There are thermoses with tea in the tents," one man told the Ukraine 24 news outlet.
(Reporting by Natalia Zinets, Simon Lewis and Matthias Williams; writing by Matthias Williams; Editing by Kevin Liffey)
