Either the Democratic Party and the People of Liberty Party “will form a grand coalition committed to reforms and changing the electoral law, which would be very difficult, or Italy will be ungovernable,” Mr. Folli added.

Mr. Monti’s caretaker government remains in place with full powers until a new government is formed. Appearing on television on Monday evening, Mr. Monti said he felt “tremendous regret” that during his tenure the political parties were not able to change Italy’s electoral law so as to guarantee more political stability. “It is a great responsibility of the political forces, and one of the reasons for the disaffection and distance from and the revindication of the political class,” he added.

Under Italy’s complex electoral laws, it is extremely hard for any one party to gain a strong ruling majority needed to manage an economy with rising unemployment and a credit crunch, let alone push through structural changes to the ossified economy. Instead, the parties have resisted change to protect their own power bases.

The results of this election would appear to represent new depths of gridlock, and few experts expected any party to form a governing coalition strong enough to prevail for long. Nicolas Véron, an economist and a senior fellow at Bruegel, a Brussels-based research institute, said that regardless of who ultimately controls the levers of government, “the key question is whether we can have serious structural reform.”

Italy “was a work in progress before the elections,” Mr. Véron added, “and I think investors understand that it will remain a work in progress for some time.”

When he came to power in November 2011, after Mr. Berlusconi stepped down amid intense market turmoil, Mr. Monti was praised for restoring international confidence in Italy. Although he won plaudits from European leaders and President Obama, Italians disliked him for raising the retirement age and taxes.

“Taxes, taxes and more taxes, that’s what voters remember the most from Monti,” said Stefano Sacchi, a professor of political science at the University of Milan. “When he stopped being a technocrat and became a politician, he came under fire for the same issues Italians blame other politicians for.”