Perera said the dissolution was carried out so that Sirisena could avoid defeat in parliament next week.
Tensions had been building between Sirisena and Wickremesinghe for some time, as the president did not approve of economic reforms introduced by the prime minister.
He also appointed new ministers - giving them access to official resources in the run-up to any vote.
Sri Lanka's ousted Prime Minister Ranil Wickremesinghe arrives at a news conference in Colombo, Sri Lanka October 27, 2018.
Sirisena's move is nevertheless set to be challenged by his opponents in the Supreme Court on Monday, with Tilvin Silva, the general secretary of the leftist People's Liberation Front (JVP), describing the action as "illegal". It said the names of candidates will be called before November 26 and the new Parliament is to convene January 17.
The US Bureau of South and Central Asian Affairs, an agency within the State Department, stated on Twitter: "The US is deeply concerned by news the Sri Lanka Parliament will be dissolved, further deepening the political crisis".
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Another witness on a passing tram told ABC Radio it seemed police had been trying to subdue a man who was waving something. It is normal for people to have strong emotional or physical reactions following a distressing or frightening event.
The EU said Friday, before the dissolution, that the crisis had scarred the Indian Ocean island's global reputation.
Following the sacking, the president suspended parliament in a move which Wickremesinghe said was meant to prevent the ousted prime minister from contesting the decision in the legislature.
A leader of Rajapakse's party, Susil Premajayantha, said Sirisena sacked the legislature to end the power struggle and allow people to elect a new parliament. Besides, it will also weaken Sirisena's bargaining power in the remaining months as President, dwindling his opportunity to run for presidency as a common candidate in an SLFP-SLPP electoral alliance.
Australia's foreign minister expressed concern and said Sirisena's action "undermines Sri Lanka's long democratic tradition and poses a risk to its stability and prosperity".
Following the unprecedented decision, Wickremesinghe refused to accept the move and sought a vote in the Parliament to prove his majority, however, Parliament was suspended and was scheduled to reconvene, it was dissolved on Friday by Sirisena.
Rajapaksa, who ruled as president from 2005 to 2015, is credited as a hero by the ethnic Sinhalese majority for winning the conflict.
Independent legal experts have told Reuters that parliament could be dissolved only in early 2020, which would be four-and-half-years from the first sitting of the current parliament.
Given those views, it was not immediately clear how Sirisena can legally dissolve parliament, though his legal experts have said there are provisions for him to do so.