Major U.S. and European stock exchanges plunged Wednesday and Italy's borrowing costs jumped, as the long shadow of the continent's debt crisis consumed the Greek and Italian governments.

Key stock markets in New York, London, Paris and Frankfurt all slid more than two percent, in part due to the political uncertainty in Athens and Rome.

Late in the day, outgoing Greek Prime Minister George Papandreou told a national television audience that he and opposition lawmakers had reached an agreement on a coalition government. The interim government will now have to carry out austerity measures demanded by the country's international creditors.

Mr. Papandreou pledged that Greece would do “whatever is required to remain” in the 17-nation bloc that uses the euro currency, and that the coalition government signals “a new future for our country.”

Meanwhile, the Italian government faced record-high borrowing costs the day after Prime Minister Silvio Berlusconi said he would resign as soon as Parliament enacts budget cuts. The spending reforms are aimed at cutting the Rome government's massive debt in hopes of avoiding the need for an international bailout.

Interest rates on Italian government bonds topped 7 percent for the first time since the advent of the euro currency in 1999. That percentage rate is the threshold at which Greece, Ireland and Portugal all were forced to secure international bailouts in the last year and a half.

Greek news accounts said that 60-year-old Parliament chief Filippos Petsalnikos has been tapped as the interim prime minister after early speculation had centered on Lucas Papademos, an economist and former vice president of the European Central Bank.

Mr. Papandreou and opposition leader Antonis Samaras had been locked in talks since Monday on who will lead a power-sharing government until early elections, tentatively scheduled for February 19, are held.

The European Union demanded that both Mr. Papandreou's socialists and Samaras' opposition New Democracy party sign a written commitment to carry out the austerity measures as part of the debt-relief plan approved for Greece last month. Samaras balked at a written statement, calling it an insult to “national dignity” and insisting his verbal assent to the plan should be sufficient. It was not immediately known whether the dispute was resolved.

European finance ministers are waiting for the formation of a new government in Greece before deciding whether to grant the country a crucial $11 billion loan installment.

In Italy, one opposition lawmaker, Giuseppe Fiorini, said the country needs a government that can give Italy “international credibility,” something he said Mr. Berlusconi has not been able to do.

One government debt analyst in London, Jan Randolph of IHS Global Insight, said investor concerns about the safety of Italian debt will not abate “until a solid and stable government actually implements austerity and undertakes reforms.”