However, Sirisena's collation partner and UNP leader Ranil Wickremesinghe told News First that despite the swearing in "I am still the Prime Minister of this country".
Both Extraordinary Gazettes have been published by the Secretary to the President Udaya R. Seneviratne on Friday (26).
Reacting sharply to the development, Minister of Finance and Media Mangala Samaraweera said that the appointment of Rajapaksa as the prime minister is "unconstitutional and illegal". Rajapaksa took the oath in front of President Maithripala Sirisena shortly after the Sirisena-led United People's Freedom Alliance (UPFA) withdrew from the national coalition government. I will function as the prime minister.
Speaking to reporters Mr Ranil Wickremesinghe siad he was still prime minister and pledged to show his majority in parliament soon. Since the constitution after the Nineteenth Amendment specifies these ways in which the prime minister ceases to hold office, and has impliedly removed the previous power of the president to remove the prime minister at will, it follows that there are no other ways in which this can happen.
Sirisena, who was Rajapaksa's minister of health, broke away from him to contest the presidential elections. He said a request had been made to the speaker to call parliament on Sunday.
A top Sri Lankan police official was arrested on Thursday over a suspected plot to kill President Maithripala Sirisena, police a spokesman said.
The unity government was formed in 2015 when Sirisena (leader of the Sri Lanka Freedom Party -SLFP) was elected President with Wickremesinghe's support, ending a almost decade-long rule by Rajapaksa. The pair were reported to have clashed in cabinet last week over government plans to lease a container terminal to neighbouring India.
There was no immediate comment from Wickremesinghe or the UNP. "This is an anti democratic coup", he said.
"We expect economic development and a good future for our children", he said.
Sirisena had pledged accountability for war atrocities, but has faced worldwide criticism for being slow to deliver on justice.
Moreover, the former president is also accused of corruption on an epic scale, along with his inner circle. Sirisena loyalists backed a no-confidence motion in April against the prime minister, who survived after a majority of legislators voted to support his coalition government.