(Bloomberg) -- Former Ukrainian President Petro Poroshenko arrived in court on Wednesday as a judge considered whether to detain him amid charges of high treason, an added dimension of political tension as the country confronts Russian troops amassing on its eastern border. 

The one-time head of state denies the accusations over deals with Russian-backed separatists, calling the charges a political attack by President Volodymyr Zelenskiy’s administration. On his return to Ukraine on Monday, Poroshenko said Zelenskiy had “crossed the red line” with the legal standoff. 

“They are afraid of us. We have a very important mission,” Poroshenko told reporters before entering the court. “We will fight for Ukraine and we will win for sure.”

A crowd of Poroshenko’s supporters gathered outside courthouse in Kyiv, demanding his release. The hearing adjourned on Monday after 11 hours of debate and deliberation by Judge Oleksiy Sokolov. Prosecutors have demanded detention in custody or bail of 1 billion hryvnia ($35.7 million). 

The hearing took place as U.S. Secretary of State Antony Blinken arrived in Kyiv for talks as Ukraine’s western allies warn of a potential Russian invasion. 

The legal standoff and the prospect of a former Ukrainian leader behind bars has led to unease among western allies over political score-settling and potential upheaval that could complicate efforts to secure unity as the country faces a Russian threat. 

The former president, who leads a party in opposition to Zelenskiy’s government, could face up to 15 years in prison if he is convicted. Poroshenko led Ukraine for five years after the 2014 Maidan uprising that toppled the country’s Kremlin-backed leader. Charges against him involve accusations of buying coal from the separatists in Ukraine’s eastern Donbas region. 

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