Thailand's new Prime Minister Srettha Thavisin took office on Wednesday, leading a coalition that includes pro-military parties with which his party had long been at odds.

The Pheu Thai Party's Srettha was endorsed by the king on Wednesday, one day after being chosen as prime minister in a parliamentary vote.

In his speech, Srettha said he will listen to the people, restore harmony in the nation, move the country forward, and create a better future for younger generations.

Pheu Thai had been calling for the elimination of military influence in politics and won the second-most lower house seats in the May general election.

But it decided to join forces with pro-military conservative parties and exclude the Move Forward Party, which won the most seats in the election. The decision has drawn criticism.

Pheu Thai is affiliated with former Prime Minister Thaksin Shinawatra, who was ousted in a military coup in 2006.

After 15 years of de facto exile, Thaksin returned to Thailand on Tuesday, the same day the new prime minister was chosen, amid speculation that a deal to pardon him has already been made.

Thaksin was sent to prison to serve an eight-year sentence for corruption and other charges. But he was taken to a hospital on Wednesday. Authorities say the 74-year-old complained he couldn't sleep well, and felt tightness in his chest.