Leaders of the rival Palestinian groups Hamas and Fatah declared Thursday a “historic day” at the conclusion of a meeting here aimed at healing a 20-month schism.

The long-awaited Cairo talks added another twist to an already complex political situation as President Obama’s Middle East envoy arrived in Israel for discussions with Israeli and Palestinian officials.

At a joint news conference in the Egyptian capital, Ahmed Qurei of Fatah and Moussa Abu Marzouk of Hamas announced the establishment of committees to find formulas for a Palestinian unity government and new elections, among other things. The committees aim to finish their work by the end of March.

Given the bitter divisions between Fatah and Hamas, it remained unclear what kind of unity government might emerge, and whether it would receive international acceptance if it was formed.

Still, representatives of the parties in Cairo said there seemed to be political will on both sides to resolve their differences.

The reconciliation talks, held under Egyptian auspices, were the first since Hamas, the Islamic militant group, took control of Gaza in June 2007, routing the Palestinian Authority forces loyal to President Mahmoud Abbas of the mainstream, secularist Fatah. Hamas took over after a brief but brutal factional war in Gaza in which scores of Palestinians were killed.

The American envoy, George J. Mitchell, is on his second trip to the region in a month, part of “ongoing efforts” to “actively and aggressively” advance the Israeli-Palestinian peace process, American officials said.

But Israeli politics were also in flux after elections this month, leaving the future of the peace process unclear.

Benjamin Netanyahu, Israel’s prime minister-designate and the leader of the conservative Likud Party, has been holding coalition talks with right-wing and religious parties as the prospect of a more centrist coalition has dimmed.

A narrow, hawkish government would be unlikely to subscribe to the same peacemaking principles as the Obama administration and the departing Israeli government, which favor a process based on establishing a Palestinian state.

Earlier Thursday, Mr. Mitchell held talks in the Turkish capital of Ankara with Prime Minister Recep Tayyip Erdogan. Mr. Mitchell said he was there because President Obama and Secretary of State Hillary Rodham Clinton “appreciate Turkey’s continuing commitment to a comprehensive peace and a two-state solution.”

In Israel, Mr. Mitchell met with leaders of the departing government and with Mr. Netanyahu. He planned to meet with leaders of the Western-backed Palestinian Authority on Friday in the West Bank.

In Cairo, 13 Palestinian groups, some of them tiny, attended the reconciliation talks mediated by the Egyptian intelligence chief, Omar Suleiman. The main purpose was to find some means of power-sharing between Fatah and Hamas.

Hamas won parliamentary elections in 2006 and formed a unity government that included representatives of Fatah. But Hamas is classified as a terrorist organization by Israel, the United States and the European Union, and that government was boycotted by Israel and the West. Mr. Abbas dissolved it after the Gaza takeover by Hamas in 2007, which he described as a coup.

Mr. Abbas’s authority has since been limited to Palestinian-controlled areas of the West Bank. For more than a year, Israel engaged in peace negotiations with Mr. Abbas aimed at laying the foundations of a Palestinian state.

At the same time, Israel imposed a strict economic embargo on Hamas-run Gaza, and it carried out a devastating 22-day military offensive against Hamas that ended last month.

The joint committees are expected to deal with the main issues in dispute: the basis for a unity government, elections, the makeup of the Palestinian security forces and reform of the Palestine Liberation Organization, the Palestinian umbrella group that has so far not included Hamas.

President Abbas has been pressing in recent months for a government made up of independent technocrats, but Hamas insists on playing a role.

Mahmoud Zahar, a senior Hamas official, said not all the issues would have to be resolved simultaneously, indicating a new degree of flexibility.

Egypt is also trying to broker a long-term truce between Israel and Hamas, as well as the release of an Israeli soldier held captive by Hamas since 2006.

Early Thursday, one of two rockets launched by Palestinian militants in Gaza hit the yard of a house in the Israeli border town of Sderot. The Israeli Air Force carried out retaliatory strikes against five tunnels used for smuggling under the Egypt-Gaza border. No injuries were reported on either side.

Taghreed El-Khodary reported from Cairo, and Isabel Kershner from Jerusalem. Sabrina Tavernise contributed reporting from Istanbul.