Thailand's prime minister has conceded defeat in Sunday's general election, won by an opposition party allied to ousted prime minister Thaksin Shinawatra.

Abhisit Vejjajiva Sunday congratulated his opponent Yingluck Shinawatra, the younger sister of former prime minister Thaksin and leader of the Pheu Thai party. She is set to become Thailand's first female prime minister.

Contrary to pre-election polls and analysis that predicted a tight race, the Pheu Thai party won an absolute majority in parliament, beating Mr. Abhisit's Democrat party in a landslide.

Results show the opposition party winning more than 260 seats in the 500-member parliament.

The United States has released a statement congratulating Thailand for voters' “robust participation” in the election.

Thailand has been deeply divided since the kingdom's military staged a bloodless coup that ousted Mr. Thaksin in 2006.

The elections were the nation's first since anti-government protests by the former prime minister's supporters last year led to clashes in which more than 90 people died.