The UK Minister of State for Asia and the Pacific Mark Field said that he was concerned by news that Sri Lanka's Parliament has been dissolved days before it was due to be reconvened.
Sirisena signed an official notification dismissing the 225-member assembly with effect from midnight, clearing the way for a snap election almost two years ahead of schedule.
President Sirisena has failed to persuade the parliament to support his ouster of his one-time ally Wickramasinghe.
The leader of Pivithuru Hela Urumaya Udaya Gammanpila earlier in the day said the President can exercise power vested with him under article 33 (2) c of the constitution to dissolve the Parliament.
The European Union in Colombo on Thursday said that it was essential that parliament be allowed to demonstrate its confidence by voting immediately when reconvened in order to resolve the serious uncertainties now facing the country.
"This is a gross violation of the constitution", Harsha De Silva, a lawmaker in Wickremesinghe's party, said in reference to the dissolution of parliament.
The party said in a Twitter message that it will meet the elections commissioner to discuss the constitutionality of Sirisena's move.
Set where ‘Westworld,’ ‘M*A*S*H’ were filmed burns in California wildfire
Quinn, Medicine Woman, American Sniper , and The Love Bug , has most recently been used by the HBO series Westworld . When not in use for filming, visitors could stroll through Western Town while hiking or ride through on horseback.
Sirisena's sweeping decisions took place Friday via a decree signed just hours after his Sri Lanka Freedom Party's coalition announced it did not have enough votes to support the leader's preferred candidate for the position of prime minister. He said the government must go to the people for confirmation on whether the president made the correct decision when he appointed him as prime minister.
Sirisena suspended parliament to give himself more time to engineer defections, according to the opposition.
Wickremesinghe is holed up in his official residence refusing to go, saying his removal would be illegal, while Rajapakse is running a parallel administration from the prime minister's office. Several legislators have said they were offered millions of dollars to switch allegiance and at least eight have already jumped to the president's side.
Under pressure from the United Nations, United States and the European Union to allow a parliament vote, Sirisena agreed three times to lift the suspension but changed his mind each time.
"Any further delays could damage Sri Lanka's global reputation and deter investors", it warned.