Poland's Prime Minister Mateusz Morawiecki denounced Belarus' diversion of the flight as "an act of state terrorism", while French Foreign Minister Jean-Yves Le Drian called for a "strong and united response" from the European Union.
The president of the European Council Charles Michel, who will host a summit of the 27 EU national leaders on Monday, also spoke out.
The Belarusian Interior Ministry initially confirmed the detention on Telegram, but the post was later deleted. The plane was closer to the Vilnius airport than it was to the one in Minsk.
Roman Protasevich (26), the detained journalist worked for an online opposition news service NEXTA, a Telegram channel that broadcast footage of mass protests against Belarus President Alexander Lukashenko past year at a time when it was hard for foreign media to do so.
Deputy air force commander Andrei Gurtsevich said the plane's crew made the decision to land in Minsk but Lithuanian President Gitanas Nauseda said the plane was forced to land there. It added that he had also ordered a Mig-29 fighter jet to accompany the aircraft.
Belarus' authoritarian leader Alexander Lukashenko declared himself the victor of an election in August to his sixth term.More news: Local Pharmacist Ready to Complete AstraZeneca Vaccinations More
Monday's European Union summit in Brussels was pre-planned, but Michel's spokesman Barend Leyts confirmed that the Belarus question would come up and "that possible sanctions will be discussed at this occasion". Borreell said Belarus must be held responsible for the safety of all passengers on the aircraft.
"The regime forced the landing.to arrest (the) journalist and activist", she wrote on Twitter.
"I call on Belarus authorities to immediately release the detained passenger and to fully guarantee his rights".
The government in Ireland, where Ryanair is headquartered, described the incident as "absolutely unacceptable", while North Atlantic Treaty Organisation called it "dangerous" and demanded an global investigation.
The move comes amid an intensifying crackdown following historic demonstrations that gripped the ex-Soviet country after a disputed presidential election a year ago.
Belta reported, citing airport official Maksim Kiyakov.More news: Dead From Extreme Weather in Gansu Ultramarathon
The airline said the plane landed safely in Minsk and passengers disembarked while security checks were carried out and that "nothing untoward" was found.
The opposition believes that Tikhanovskaya, who fled to neighbouring Lithuania after the election, was the true victor of last year's presidential vote.
Pratasevich has lived in Lithuania since November.
"Then when the plane had entered Belarus airspace, the KGB officers initiated a fight with the Ryanair crew insisting there's an IED onboard", he said. On the ground, security agents arrested Roman Protasevich, founder of the social media news channel, NEXTA, which played a crucial role in the protests last summer. But Lithuanian Foreign Minister Gabrielius Landsbergis said there were 171.
The EU and the United States have sanctioned Lukashenko and dozens of officials and businessmen tied to his regime with asset freezes and visa bans.
Belarus's most popular news website, Tut.by, went offline last week as authorities intensified their attack on independent media.More news: Britain’s Prince William gets first dose of Covid-19 vaccine