Sri Lanka's newly elected president is set to name his brother and current opposition leader Mahinda Rajapaksa as interim prime minister, a party spokesman said on Wednesday, just hours after the sitting premier said he plans to step down.

Premier Ranil Wickremesinghe said he planned to tender his resignation on Thursday, after his party's candidate lost in a presidential election to Mahinda's younger brother Gotabaya Rajapaksa over the weekend.

Mahinda Rajapaksa will be sworn as prime minister and assume office on Thursday, Keheliya Rambukwella, a spokesman for the Mahinda-led Sri Lanka Podujana Peramuna (SLPP), told Reuters.

This will see two brothers holding the top positions in the government of Sri Lanka for the first time in its history.

Gotabaya Rajapaksa, also a member of the SLPP, defeated the candidate from Wickremesinghe's party on Nov. 16. Gotabaya had earlier served as defence chief under his brother Mahinda, who himself served as president from 2005-2015.

"I have decided to resign from the Prime Minister's post to give space for the new President to form his own government," Wickremesinghe said earlier on Wednesday.

Government leaders said a parliamentary election is expected around April and Mahinda is expected to be his party's prime ministerial candidate.

Security Concerns

The recent presidential election was largely overshadowed by Sri Lanka's deepest economic slump in more than 15 years, which followed attacks on hotels and churches on Easter Sunday that killed more than 250 people. Islamic State claimed responsibility for the attacks, which damaged Sri Lanka's important tourism sector.

Gotabaya, who oversaw the defeat of Tamil separatists as his brother's defence chief a decade ago, won the election after promising to secure the country against militant threats.

Under the constitution, Wickremesinghe's government will be dissolved following his resignation.

Neither Wickremesinghe's UNP, nor Mahinda Rajapaksa's SLPP has an absolute majority in parliament to form a government. Mahinda Rajapaksa attempted to return to office last year as prime minister but was blocked by a court.

The new president is expected to appoint a 15-member interim cabinet until the election.

In his first appointments, Gotabaya on Tuesday named P. B. Jayasundera, who was treasury chief under his brother, as his secretary, and tapped close ally Kamal Gunaratne, a military general, as defence secretary.

Rajapaksa's election has raised hopes among investors that Sri Lanka's economy will recover. The main stock index has risen 1.9% and the Sri Lankan rupee has gained 0.5% in the past three sessions.

"What is expected from Rajapaksa was the political stability and the change in the cabinet will help that sentiment and the market will see it positively," said Dimantha Mathew, head of research at brokerage firm First Capital Holdings.

Some rights groups and minorities, however, accuse the Rajapaksas of human rights violations during the end of the 26-year civil war and have expressed concerns of renewed ethnic tensions on the island following the elections.

The Rajapaksa brothers have denied wrongdoing.