BANGKOK, Thailand — Thailand’s prime minister was ousted Tuesday after weeks of protests closed the capital’s airports, stranding 300,000 travelers. Protesters promised to lift their siege, and international flights were expected to resume Friday.

The government of Prime Minister Somchai Wongsawat was doomed when the nation’s Constitutional Court dissolved Thailand’s top three ruling parties for electoral fraud in the 2007 vote that brought them to power. Somchai was banned from politics for five years.

Somchai did not formally resign, as the protesters had demanded for months, but accepted the ruling.

“It is not a problem. I was not working for myself. Now I will be a full-time citizen,” he told reporters in Chiang Mai, the northern city where his paralyzed administration has been forced to govern since Wednesday.

Protest leaders said the airport seizures would end Wednesday.

With the waning of the political crisis, the official in charge of Thailand’s airports said Suvarnabhumi international airport will resume operations on Friday.

“Please have confidence in us,” said Vudhibhandhu Vichairatana, the chairman of the Airports of Thailand.

He called the flights a birthday gift for Thailand’s revered King Bhumibol Adulyadej, who turns 81 on Dec. 5. The airport reopened to cargo flights Tuesday.

Officials had earlier said the airport would not reopen for commercial flights before Dec. 15, but Vudhibhandhu said he brought forward the date because an inspection revealed the airport had suffered no damage and could become operational more quickly.

After Tuesday’s court decision, government spokesman Nattawut Sai-kau said the six-party governing coalition would step down.

Despite the appearance of a smooth political transition, the ruling is expected to widen the dangerous rift in Thai society that many fear could lead to more violence between pro- and anti-government groups.

Late Monday, an explosive device fired from an elevated highway fell among hundreds of protesters inside Don Muang airport, killing one person and wounding 22. The death raised to seven the number of people killed in bomb attacks, clashes with police and street battles between government opponents and supporters.

On hearing the court’s decision, a cheer rose from thousands of members of the People’s Alliance for Democracy occupying the international airport.

“My heart is happy. My friends are very happy,” said Pailin Jampapong, a 41-year-old Bangkok housekeeper choking back tears as she jumped up and down.

“This is a blow for corruption,” said Nong Sugrawut, a 55-year-old businessman at Suvarnabhumi.

Somchai had become increasingly isolated in recent weeks. Neither the army, a key player in Thai politics, nor the country’s much revered king offered firm backing.

But hundreds of his supporters gathered outside the court, saying the swiftness of the ruling — which came just an hour after closing arguments ended — appeared predetermined. At one point they cut off the power supply to the court, but electricity was restored with diesel generators.

“The court is not qualified to make this ruling. They are nothing more than apologists for the alliance, who are ruining the country,” an activist shouted through a megaphone outside the court.

Somchai’s People’s Power Party, the Machima Thipatai party and the Chart Thai party were found guilty of committing fraud in the December 2007 elections that brought the coalition to power.

“Dishonest political parties undermine Thailand’s democratic system,” said Court President Chat Chalavorn.

The ruling sends Somchai and 59 executives of the three parties into political exile and bars them from politics for five years. Of the 59, 24 are lawmakers who will also have to abandon their parliamentary seats.

But lawmakers of the three dissolved parties who escaped the ban can join other parties, try to cobble together a new coalition and then choose a new prime minister.

Until then, Deputy Prime Minister Chaowarat Chandeerakul will become the caretaker prime minister, said Suparak Nakboonnam, a government spokeswoman. She said parliament will have to pick a new prime minister within 30 days.

The protesters accuse Somchai of being a proxy of ousted Prime Minister Thaksin Shinawatra, the alliance’s original target. Thaksin, who is Somchai’s brother-in-law, was deposed in a 2006 military coup and has fled the country to escape corruption charges.

Alliance supporters are largely middle-class citizens who say Thailand’s electoral system is susceptible to vote-buying and argue that the rural majority — the Thaksin camp’s political base — is not sophisticated enough to cast ballots responsibly.

They have proposed discarding direct elections in favor of appointing most legislators, fostering resentment among rural voters.

The protest leaders have been charged with several criminal offenses, but are out on bail, and it is not known when they will be tried.