Luigi Di Maio, leader of the populist Five-Star Movement on Friday claimed that talks on a cabinet with far-right League party leader Matteo Salvini and premier designate Giuseppe Conte were "going very well".
"The talks have gone very well. There is total synergy!" Di Maio told reporters at the parliament in Rome.
"We are working rapidly to ensure a government of change takes office as soon as possible," he said.
"There is a lot of unity," Di Maio added.
"Conte, Salvini and I understand each other straight away," he said, declining to comment on alleged 'dikats' and vetos during the negotiations.
Conte, Di Maio and Salvini were on Friday hammering out the list of proposed ministers that Conte is due to present to Mattarella for his approval.
Italy has been in political limbo since the inconclusive 4 March national polls in which populist parties made strong gains but no single political force won a outright parliamentary majority.
Five-Star is the biggest party while the centre-right alliance led by Salvini is the largest political bloc. Mattarella on Wednesday invited Conte - Salvini and Di Maio's pick of prime minister - to try and form a government.
