A train carrying the former president of Georgia and one-time governor in Ukraine Mikheil Saakashvili has been stopped on its way to Ukraine.
Mr Saakashvili is a stateless person, having had his Ukrainian citizenship stripped by his former ally, President Petro Poroshenko, after a falling out.
He is also wanted in Georgia on criminal charges, which he claims are politically motivated.
His train was held at a railway station in Przemysl, Poland.
It is not clear who ordered the train to be stopped. AFP news agency quoted the operator of the train as saying she had been ordered by the authorities, but declined to specify whether they were Polish or Ukrainian.
Mr Saakashvili was joined by a number of his supporters, including former Ukrainian Prime Minister and current opposition leader Yulia Tymoshenko.
Mr Saakashvili, who was born in Georgia, said he is returning to his adopted Ukraine to contest President Poroshenko’s decision to strip him of his citizenship in July while he was out of the country.
In 2015, he was appointed governor of Odessa by Mr Poroshenko, but the two fell out last November after Mr Saakashvili accused the president of blocking efforts to stop corruption.
But in accepting Ukrainian citizenship, he surrendered his Georgian citizenship.
“The reality is for me today that the Georgian passport means guaranteed imprisonment for me in Georgia,” he told the BBC at the time.
If he crosses in to Ukraine, he could possible be arrested and deported to Georgia to face charges, the BBC’s Europe Regional Editor, Danny Aeberhard, said.
But Mr Saakashvili has been adamant about his return to rally political supporters, having announced his return to the country as far back as July.
Ukraine is a signatory to the UN Convention on the Reduction of Statelessness, which prohibits the withdrawal of citizenship when doing so would result in a person becoming stateless.
Exceptions exist in limited circumstances such as fraud or disloyalty to the state, though it is not clear if either apply in Mr Saakashvili’s case.
Ukraine’s migration service said the president takes decisions on who is stripped of Ukrainian citizenship based on the conclusions of the citizenship commission.
It did not provide the exact reason, but stated that this could be done if a Ukrainian national acquired citizenship of another country or submitted false documents.