(Bloomberg) -- A Ukrainian court adjourned a hearing on the detention of former President Petro Poroshenko, who is under investigation for committing high treason in deals with Russian-backed separatists last decade.

The legal standoff pressed by President Volodymyr Zelenskiy’s administration injects a level of political instability in the region as Russian leader Vladimir Putin amasses troops on Ukraine’s eastern frontier, a move that’s prompted Western allies to raise the specter of a full-scale invasion. Russia has repeatedly said it doesn’t plan to invade. 

Poroshenko led Ukraine for five years after the 2014 Maidan uprising that toppled the country’s Kremlin-backed leader. He now faces accusations of buying coal from the separatists in Ukraine’s eastern Donbas region. Still active politically, he leads a party in opposition to Zelenskiy.

The former leader returned to Kyiv from abroad on Monday to fight the charges, accusing Zelenskiy of crossing a “red line” with the allegations, which he denies.

After a six-hour courtroom debate, and another five hours in which Judge Oleksiy Sokolov considered a ruling in chambers, the court adjourned and said it would resume the hearing on Jan. 19. Prosecutors have demanded detention in custody or bail of 1 billion hryvnia ($35.7 million). 

Poroshenko left the court after the adjournment and addressed hundreds of supporters outside who had called for his release. 

“This will become the beginning of end for their stupid, populist era,” he told the crowd. “One can’t split the country when an enemy, Putin, is at the gate.”

Political Clash

It’s a dramatic shift of fortune for Poroshenko, the chocolate-magnate-turned-politician lauded by the U.S. and European Union for his tilt toward the West in the years after President Vladimir Putin’s seizure of Crimea from Ukraine. Poroshenko stood for greater integration with the EU and NATO while Putin broke fully from the West.

But the wealthy tycoon has come under the scope of Zelenskiy’s administration, which has made a concerted effort to curb the political influence of oligarchs and stem endemic corruption. 

Late last year Zelenskiy took aim at Ukraine’s richest man, Rinat Akhmetov, who has vast holdings in the country’s east, as well as its largest private power utility, DTEK. Akhmetov was being dragged into a Russian-backed coup attempt against him, Zelenskiy claimed, a charge the billionaire strongly rejected. 

The maneuvering has led to unease among western allies that potential political chaos in Kyiv could complicate efforts to secure unity as the country faces a Russian threat. 

Carl Bildt, the former Swedish foreign minister, fretted in a tweet Saturday that Zelenskiy was “more focused on arresting” Poroshenko than uniting the country. 

The U.K.’s top envoy to Ukraine echoed the sentiment. 

“All political leaders in Ukraine need to unite against Russian aggression right now,” British Ambassador Melinda Simmons posted on Twitter. “So important at this time not to lose sight of this or be distracted by polarising domestic politics.” 

A court previously ordered the seizure of Poroshenko’s assets, including real estate and companies listed in the state registry, prompting the former president and his allies to cry foul at what they called a politically motivated attack. 

Tetyana Sapyan, a spokeswoman for the State Bureau of Investigations, denied allegations of a political motive behind the case.

“Politics are for politicians, and facts are for detectives,” she said on Monday. “The investigation is on.” 

Poroshenko, who is worth $860 million according to the Bloomberg Billionaire Index, is accused of using state finances to buy coal from mines controlled by Donbas separatists in 2014 and 2015, impeding diversification of energy sources and causing increased dependency on Russia. 

(Updates with context, background from second paragraph.)

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