Long-delayed results of Thailand's first election since a 2014 military coup released on Wednesday produced no clear winner but gave a pro-army party a clear advantage in its bid to install the current junta leader as an elected prime minister.

The opposition threatened legal action against Wednesday's results, saying that a new seat allocation formula robbed the "democratic front" alliance of a majority in the 500-seat House of Representatives.

The results are likely to set up a period of coalition building, since neither the pro-military bloc of parties nor a "democratic front" opposition alliance so far has enough votes to elect a prime minister under rules written by the junta.