Leftist leader Pier Luigi Bersani got the formal go-ahead on Friday to try to form Italy's next government after his coalition won elections last month but failed to get an overall majority.
"I have asked Bersani to verify whether he has the parliamentary support required to form a new government. He will report back to me as soon as possible," President Giorgio Napolitano said after two days of consultations with political leaders.
"Today marks the start of a decisive phase in giving Italy a new government," Napolitano said, warning against "sterile delays" in a difficult road ahead.
"We can no longer ignore the spread of social unease and the expressions of dissatisfaction against political parties," he said, referring to the high number of protest votes in the February 24-25 elections as Italy endures a deep recession.
Napolitano indicated he would have favoured a "grand coalition" between Bersani's centre-left and Silvio Berlusconi's centre-right but said the obstacles to this "appear significant".
He called for "a spirit of national cohesion".
Bersani said he would meet with lawmakers "straight away" to build a majority, saying: "I'll take the time I need in a difficult situation."