A train carrying former Georgian President Mikhail Saakashvili and his supporters was prevented from leaving a railway station in Poland for Ukraine on Sunday, deepening a standoff between Saakashvili and Ukrainian authorities.

Saakashvili intended to return to Ukraine despite being stripped of Ukrainian citizenship by his one-time ally, Ukrainian President Petro Poroshenko, and being threatened with arrest and extradition if he sets foot on Ukrainian soil.

Poroshenko invited Saakashvili to become a regional governor in Ukraine to help drive reforms after prodemocracy protests in 2014 ousted pro-Russian President Viktor Yanukovych from Kiev.