Sri Lankan Prime Minister Ranil Wickremesinghe will resign this week, a spokesman from his office said on Wednesday, after his party's candidate lost a presidential election over the weekend.
Sources had earlier told Reuters that Wickremesinghe's exit was imminent and local media separately reported that the new president, Gotabaya Rajapaksa, would soon name an interim cabinet to govern the island until a parliamentary election, expected around April.
"The resignation letter will be sent (to the president) by tomorrow," Sudharshana Gunawardena, a spokesman for Wickremesinghe said.
Former wartime defence minister Rajapaksa of the Sri Lanka Podujana Peramuna (SLPP) won the presidency by a significant margin in Saturday's vote, defeating former housing minister Sajith Premadasa, the candidate of Wickremesinghe's United National Party (UNP)-led coalition.
The presidential election was overshadowed by Sri Lanka's deepest economic slump in over 15 years after Easter Sunday attacks on hotels and churches killed more than 250 people. This caused a crisis in the tourism sector, a vital source of foreign exchange. Islamic State claimed responsibility for the attacks.
Rajapaksa, who oversaw the defeat of Tamil separatists under his brother and then-president Mahinda Rajapaksa 10 years ago, won the election after promising to secure the country against militant threats.
Under the Sri Lankan constitution, Wickremesinghe's government will be dissolved following his resignation.
Neither the UNP nor the opposition SLPP, which is led by Rajapaksa's elder brother Mahinda, the former president, has an absolute majority in parliament to form a government.
Rajapaksa is expected to appoint a 15-member interim cabinet until the parliamentary election, when his brother is expected to seek the post of prime minister.
Some local media reported on Wednesday that the new president would name his brother as interim prime minister, until the election.