Hundreds of people in Poland and Lithuania gathered for protests on Saturday to show support for the opposition in neighbouring Belarus.
They called for the release of a Belarusian dissident who was arrested along with his girlfriend when their flight was diverted to Minsk.
The pair's detention sparked global outrage and prompted the EU to urge airlines to avoid Belarusian airspace.
Protests took place elsewhere in Europe as well as in the US and Australia.
Roman Protasevich, 26, and Sofia Sapega, 23, were flying from Greece to Lithuania on Sunday when a fighter jet was scrambled over Belarus to escort their plane to Minsk airport over a bomb threat that turned out to be fake.
They were arrested as soon as the Ryanair plane landed.
"I'm calling on all EU countries and the US to please help us free Roman and Sofia, as well as everyone else imprisoned," Mr Protasevich's mother, Natalia, said at a rally in the Polish capital Warsaw.
"We want to live in a free country, in a country where everyone has the right to express his beliefs," his father, Dmitry, added.
The crowd at the Warsaw rally waved the Belarusian opposition's red and white flag and held signs that read Help Belarus and Freedom for Belarus.
"Things look really bad now. That's why we need to do something, show those fighting back home that they're not alone," Natallia Burak, a 35-year-old Belarusian living in the city, told the AFP news agency.
"As a Belarusian, we see a lot of wild and outrageous things," another demonstrator added.
Belarusian President Alexander Lukashenko, who has been in power for 27 years, has been nicknamed "Europe's last dictator". The 66-year-old has cracked down on dissenting voices, and many opposition figures have been arrested or fled into exile.
One such figure is the opposition leader Svetlana Tikhanovskaya, who spoke at a rally in Lithuania where she has been living in exile since last August.
"I believe that there will be changes very soon, there will be new elections, because there can be no other way," she told a crowd gathered in the capital, Vilnius. "Belarus will not give up."
Ms Tikhanovskaya and several hundred protesters marched to the Belarusian embassy in the city.
A similar demonstration also took place in Berlin, while smaller protests were seen in dozens of countries including Ukraine, Ireland, and the Netherlands.