Former Italy PM Silvio Berlusconi says it is crucial to form a strong government.
Italy's parliament convenes on Friday almost three weeks after last month's inconclusive election.
The centre left is strongly leading in Italy's election, 5-6 percentage points ahead of the centre right.
Italians began voting on Sunday in one of the most closely watched elections in years.
Silvio Berlusconi sent letters to millions of Italians promising to reimburse tax they paid in 2012.
Italy PM Mario Monti said he was unlikely to agree to serve as a minister after the elections.