Former Ukrainian President Petro Poroshenko has been stopped at the border with Poland amid suspicions he was trying to escape his war-torn country to avoid fighting.
With martial law currently in place across Ukraine, male citizens aged 18 to 60 are subject to mobilisation and cannot go abroad.
The law is expected to stay in place across the country until at least August 23.
Poroshenko, a 56-year-old reserve serviceman, was famously filmed brandishing a rifle as he walked through Kyiv earlier on in the war in an apparent show of patriotism.
But now it is suspected he was trying to leave the country, possibly to avoid fighting, after he was prevented from crossing the border with Poland twice.
Another reason mooted for his attempt to leave Ukraine is that he is currently accused of state treason, aiding terrorist organisations and financing terrorism.
The accusations were made in December last year, after the former leader allegedly organised the purchase of coal from separatist-controlled areas of Ukraine.
He won a court ruling the following month allowing him to remain at liberty while being investigated on the criminal charges, which he says are politically motivated.
But Poroshenko, who was President of Ukraine from June 2014 to May 2019, has denied he was trying to cross the border for any of these reasons.
In a statement on Sunday, he addressed the nation with his political adversary: "Dear Mr President [Volodymyr Zelenskyy]!
"I am addressing you on my way from Kyiv to the Congress and the Summit of the European People's Party, the most influential political family in Europe, whose members are the leadership of the EU structures and many member states.
"It is there that decisions will be made, among other things, on the prospects of strengthening the sanctions regime against Russia, on the mechanism of post-war reconstruction of Ukraine, and on the possibility of granting our country candidate status for EU membership at the European Council in late June.”
He went on to claim he had an official invitation from the President of the European People’s Part to a business trip that had been signed by the Chairman of the Verkhovna Rada [Supreme Council] of Ukraine.
He also had speeches at the EPP Congress and Summit, a series of meetings with EU leaders, states and governments and leaders of European parties planned, he said.
"After my trip as an official parliamentary delegation to the NATO Parliamentary Assembly, where I intended to defend Ukraine's MAP [NATO Membership Action Plan] at this year's Alliance summit, was completely illegally disrupted, I hope that conclusions have been reached and no one will stop me from going to Rotterdam,” he continued.
"Against the background of the external threat, it is extremely important to maintain the unity and coordination of our efforts, to avoid any internal strife and to work together on all possible international platforms, especially such important ones as the European People's Party.
"I would like to emphasise that the main message with which I am heading to Rotterdam is to give Ukraine the status of a candidate country for EU membership in June, which symbolically coincides with the fifth anniversary of the visa-free regime.
"The second message is to support Ukraine in repelling Putin's aggression and restoring territorial integrity. This is our common war, so give Ukraine more weapons and more sanctions to the Russian fascists!
"The third message is the provision of sufficient financial assistance to our country during the war and the approval of the Marshall Plan 2.0 for post-war reconstruction.
"With such clarity in goals and messages, whose interest is it to stop me at the border?
"The Ukrainian people in these difficult times deserve the wisdom of politicians. The key to our success has always been a strong army, internal unity, strong international support and solidarity.
"And today, all together - the government, the opposition and civil society - are working to build a strong, independent, democratic, prosperous European Ukraine.
"Together we will win.
"Glory to Ukraine!"
Ukrainian media reported that Poroshenko was not allowed to cross the border because of "technical problems" with a permit allowing him to leave Ukraine.
Poroshenko made headlines last month when he publicly said Russia was on course to be a "very, very big North Korea" unless it ditched Vladimir Putin.
Petro Poroshenko, who was in office between 2014 and 2019, said he had extensive dealings with the Russian president - but said the Russian leader never delivered on promises.
Mr Poroshenko said ordinary Russians would soon come to feel the effect of devastating sanctions, adding that he is "absolutely confident that Russia has the fate of a very, very big North Korea".
In an interview with Newsweek he said world leaders must commit to "de-Putinize Russia".
Comparing Russia to Kim Jong-un's regime in North Korea, he said that citizens have "no freedom, a dictatorship, full control of mass media, unhappy and poor people".
