By ISABEL KERSHNER

JERUSALEM — President Mahmoud Abbas of the Palestinian Authority asked Rami Hamdallah, the prime minister, on Thursday to form a “government of national consensus” that would unite warring Palestinian factions for the first time in seven years and could send Israeli-Palestinian relations into a tailspin.

The new government, made up of politically independent professionals, would formally ally Mr. Abbas’s Palestine Liberation Organization, which is dominated by the mainstream Fatah faction, and its rival, Hamas, the Islamic militant group that controls Gaza, under the terms of a unity pact reached last month. Palestinian officials said the new government would most likely be announced in the next few days, with Palestinian elections to be held in about six months.

“This letter designates Dr. Rami Hamdallah to form a new transitional government,” Mr. Abbas said on Thursday at an appearance with Mr. Hamdallah, according to WAFA, the official Palestinian news agency. “I wish him luck in this difficult task which he will undertake.”

The possibility has disrupted any prospect of a resumption of American-brokered peace talks and already prompted stern warnings from Israel, which says it will not deal with a government “backed by Hamas,” even if the ministers themselves are not politically affiliated. Hamas has refused to recognize Israel, which, like the United States and the European Union, classifies Hamas as a terrorist organization.

“We think that by embracing Hamas, Abbas is increasing the levels of volatility and danger,” an Israeli government official said, requesting anonymity because he was speaking before a new Palestinian government had been formally announced. “We are concerned that Hamas will exploit the pact to strengthen its position in the West Bank.”

But Muhammad Shtayyeh, a close aide to Mr. Abbas, said that the Palestinian fragmentation had to end.

“The political program of this government is going to be the political program of President Abbas and the P.L.O.,” he said by telephone. “Hamas is coming over to our course — we are not going over to theirs.”

The Israeli official said that once Mr. Abbas “consummates” his alliance with Hamas, he could be held accountable for any rockets fired against Israel by militants in Gaza. “He will become an address for our response,” the official said, refusing to elaborate.

After the unity pact between the Palestinian factions was announced in April, Israel broke off peace negotiations with Mr. Abbas, days before the expiration of the American-brokered talks. Israel said it would deduct money from the monthly transfer of tax revenue it collects on behalf of thePalestinian Authority to offset Palestinian debts to Israeli utility companies. Israel also limited meetings between Israeli and Palestinian officials.

Once the Palestinian government of national reconciliation is formed, Israel is expected to take further steps. In the past it has stopped the transfer of tax revenue altogether, putting the financially fragile Palestinian Authority under intense pressure.

The European Union, which gives substantial aid to the Palestinian Authority, has said it will support a new government of technocrats and continue direct financial assistance so long as the government upholds international principles of nonviolence, accepts previous agreements with Israel and recognizes Israel’s right to exist.

Mr. Abbas has said that the government would adhere to these conditions. But Israel insists on Hamas adhering to them as well.

Israeli officials have said they received a specific commitment in the pastfrom the American administration that it backed Israel’s position of not negotiating or dealing with a government in which Hamas played a role unless Hamas accepted those international principles. But more recent signals from Washington raise doubts about the Israeli assertions.

After the Palestinians announced their unity deal in April, Jen Psaki, a State Department spokeswoman, called the move “disappointing.” She added that “any Palestinian government must unambiguously and explicitly commit to nonviolence, recognition of the state of Israel, and acceptance of previous agreements and obligations between the parties,” without mentioning Hamas.

“Clearly there are differences of opinion between Israel and the United States,” said Michael Herzog, a fellow of The Washington Institute for Near East Policy and a former military official and negotiator based in Israel. “Even if there were such understandings,” he said, referring to the Israeli assertions about a past commitment, “the U.S. is not there today.”

With the Obama administration already laying much of the blame for the collapsed peace talks on Israel, Washington may not support Israeli sanctions and punitive actions against the Palestinians, he said, and they may be met with additional unilateral moves by the Palestinians to join more international organizations, despite Israeli objections. There could also be a push in Congress to stop funding the Palestinian Authority.

“This new Palestinian government will inject some new tensions between Israel and the United States, adding to the existing tension after the collapse of the talks,” Mr. Herzog added.

Should the unity deal fall apart, Israel said it would resume talks with its Palestinian interlocutors. But Mr. Abbas has said that any resumption of talks depends on a three-month freeze of all Israeli settlement construction and talks that focus on the borders of a future Palestinian state. Israel has rejected these conditions.

The Vatican announced on Thursday that a prayer meeting between Pope Francis, Mr. Abbas and President Shimon Peres of Israel, who plays a largely ceremonial role, will take place in Vatican City on June 8.

For the Palestinians, national reconciliation is popular after seven years of schism. The rivalry between Hamas and Fatah peaked in 2007 when Hamas took control of Gaza a year after it won Palestinian elections and after a brief but bloody factional war in the Palestinian territory. Hamas routed the forces loyal to Mr. Abbas, whose authority was limited to parts of the Israeli-occupied West Bank. There have been no elections since.

Mustafa Barghouti, an independent Palestinian politician who took part in the reconciliation talks, said in a telephone interview that “the most important thing is that this government will mean the end of this terrible division and it will reactivate the Palestinian democratic system.”

Mr. Barghouti added that the new government would open the way for negotiations with the Egyptian government on new security arrangements that would allow the opening of the Rafah crossing on Gaza’s border with Egypt. That, he said, would begin to alleviate the crushing isolation of Gaza, caused largely by Israel’s closure of the territory. The new government in Egypt has also been squeezing the Hamas-run enclave.

Many of the thorniest issues, like the future of Hamas’s armed forces and the payment of 40,000 employees of the Hamas government, remain unresolved.

The new Palestinian government “will create an opening for discussions on these issues,” Mr. Barghouti said.

Still, Gaza will remain separated from the West Bank by 25 miles of Israeli territory at the narrowest point, with Israel strictly controlling movement between the two territories.