On Friday, 119 lawmakers in the 225-member parliament signed a letter urging Speaker Karu Jayasuriya to reconvene the body immediately. UN Chief "offered assistance in facilitating a dialogue with all the parties to resolve the situation", his office added.
The United States and the European Union have urged the president to immediately summon Parliament and let lawmakers decide who is to lead the country.
Prime Minister Mahinda Rajapaksa's legislator son Namal Sunday indicated that the long-held demand of the Tamil minority community to release all Tamil prisoners may be fulfilled soon, a move aimed at persuading the Tamil legislators to support Rajapaksa.
Rajapaksa led Sri Lanka to a military defeat of Tamil separatist guerrillas in 2009 but has since faced widespread allegations of human rights abuse and targeting of Tamil civilians.
Wickremesinghe was sacked by President Sirisena on October 26.
A police informant, Namal Kumara, who first spoke of the alleged plot, told reporters that Wickremesinghe and his Cabinet colleague, former army commander Sarath Fonseka, were behind it. Kumara claims he has a taped conversation with a senior police officer who allegedly discussed assassinating Sirisena and the former defence secretary, Rajapaksa's brother. There was confusion since Thursday on the date when the parliamentary deadlock would end as Sirisena had suspended the sittings until November 16. Rajapaksa is credited as a hero by Sri Lanka's ethnic Sinhalese majority for ending the conflict.
On Friday, the speaker of parliament said Sirisena had agreed to summon a session on Wednesday next week. Wickremesinghe's United National Party said they have handed over a motion of no-confidence against Rajapaksa. 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.
Mr Wickremesinghe said his party will step up a public campaign for Parliament to be called and he be allowed to prove his majority.