Ukraine’s ex-President Petro Poroshenko said he had been stopped from leaving the country Friday morning in what he described as a politically motivated bid to disrupt his work.

Poroshenko, who led Ukraine from 2014 to 2019 and is now an opposition lawmaker, posted a video of himself at a border crossing with Poland, saying he had been turned away and holding up papers that he said showed he had official permission to cross.

Under martial law, Ukrainian officials must get special approval to travel abroad.

The Ukrainian parliament’s deputy speaker, Oleksandr Korniyenko, later confirmed he had cancelled Poroshenko’s permission to leave the country.

Korniyenko said that while lawmakers were allowed to travel for party political events, he had received a letter, which he could not comment on, that led him to cancel the permission for Poroshenko’s trip.

The dispute comes amid slowly growing tensions between government and opposition — mostly over internal matters such as budgets and appointments — as the war against invading Russian troops grinds on, in contrast to the near-total unity at the start of the conflict.

Poroshenko said he had planned to travel to Poland to help negotiate an end to a truckers’ blockade and then to the United States to build support for Ukraine’s war effort.

Alongside his video post, he wrote a message accusing Ukrainian President Volodymyr Zelenskyy’s administration of cancelling the permission and playing politics ahead of elections.

“This is an anti-Ukrainian diversion,” Poroshenko wrote. “It is not just the hampering of my entire team’s diplomatic work, but unfortunately a blow to Ukraine’s defense capabilities.”

Zelenskyy’s office did not immediately reply to a request for comment.

Poroshenko, who leads the European Solidarity opposition party, is a prominent critic of Zelenskyy’s administration.

The two men fought a bitter, often deeply personal, battle in the 2019 presidential election when Zelenskyy defeated the incumbent Poroshenko in a landslide.

Zelenskyy told Ukrainians last month that it was “not the time” to hold a presidential election, which under normal circumstances would be scheduled for March 2024 but is prohibited under martial law.