Sirisena had replaced him with former strongman Mahinda Rajapaksa and suspended Parliament until November 16 in an apparent attempt to give Rajapaksa time to muster enough support to survive any no-confidence vote.
Attempts to win over MP defectors intensified in Sri Lanka's constitutional crisis Saturday amid growing pressure to let the suspended parliament hold a vote on the two rivals who each claim to be prime minister.
Al Jazeera's Bernard Smith reports from Colombo.
President Sirisena is the leader of the UPFA.
Adding an extra flair of global drama to everything is that President Sirisena recently alleged that a shadowy assassination plot was being hatched against him, which he confirmed on Sunday was the main reason why he sacked his Prime Minister. During this meeting, the President apprised the United Nations representative regarding the prevailing political situation in Sri Lanka.
Everything flawless for Winx on Plate eve
On Thursday I rang a few close mates to have a bit of a chat, I just try to do things to keep my mind occupied. For Winx , this win makes it 29 in a row.
Lawmakers from Rajapaksa's party have denied the allegations.
A lawmaker from the main Tamil party defected to the Rajapaksa side and was made a minister on Friday. Moreover, Wickremesinghe's popularity began to wane after his government signed an agreement giving a Chinese company an 80% stake and a 99-year lease of a failing port, seeing it as a way to avoid defaulting on Chinese loans.
The TNA's parliamentary strength has been reduced to 15 as a result and there was speculation that at least 4 more of them were willing to support Rajapaksa.
Investigations into alleged crimes and corruption by Rajapaksa's family members, his former Cabinet members and political officials could be dropped by the new Rajapaksa-led government. He is credited with ending a 25-year civil war.
"The government got GSP on the basis of certain commitments, if these commitments are not met, then we would consider withdrawal,"EU ambassador to Sri Lanka, Tung-Lai Margue, was quoted as saying to Reuters, a news agency". Rajapaksa's return could increase China's clout in Sri Lanka. Sirisena replaced Prime Minister Wickremesinghe for Rajapaksa last Friday, and suspended the Parliament after Wickremesinghe sought an emergency session to prove his majority in the legislature. Thousands of Sri Lankans also protested in the capital in the past week demanding Sirisena immediately convene Parliament. Parliament will be reconvened on the 5th of November.