UNITED NATIONS — A new Lebanese civil war could result from the United Nations’s moves to end Syria’s hegemony in Lebanon, Damascus and its allies in Beirut are warning. In Gaza, Palestinian Arab factions are threatening to drag Israel into their own civil war.

President Assad of Syria has told Secretary-General Ban that the establishment of a U.N.-backed international tribunal to try suspects in Lebanon’s political assassinations will lead to a Lebanese civil war, Mr. Ban said yesterday at the traditional mid-month luncheon of U.N. Security Council ambassadors, according to one participant. One of Syria’s main allies in Beirut, President Lahoud, made similar statements yesterday. Nevertheless, the American ambassador to the United Nations and this month’s Security Council president, Zalmay Khalilzad, said America and its allies will move quickly to pass a resolution enforcing the establishment of the tribunal.

In southern Israel, at least 20 Israeli civilians were treated for injuries yesterday after two dozen Kassam rockets were fired from Gaza amid intensifying battles among Palestinian Arab familial and political factions. At least 16 Gaza residents died in the fighting. The escalation forced Prime Minister Olmert’s government — already under public scrutiny for its indecisiveness during the Israeli-Hezbollah war in Lebanon last year — to consider whether to re-enter Gaza in an attempt to end the violence. Late last night, according to Israeli press reports, Defense Minister Amir Peretz allowed army commanders a “free hand” to fire on targets in Gaza, but he barred ground operations in the area.

On Monday, Prime Minister Siniora of Lebanon officially asked Mr. Ban and the Security Council to make a “binding decision” to establish the international tribunal to try suspects in his country’s political assassinations, including the February 2005 killing in Beirut of a former Lebanese prime minister, Rafik Hariri.

Syria and its allies are said to fear that if such a tribunal is set up, several Syrian officials — including members of Mr. Assad’s inner circle, whom U.N. investigators have cited as possible suspects — will be prosecuted, threatening its Baathist regime’s grip on power and its control over Lebanon.

Imposing the tribunal would “drag” the Security Council into “siding with one Lebanese party against the other,” Mr. Lahoud warned yesterday in a televised statement in Beirut.

But Mr. Ban told reporters that after consulting with Mr. Assad, Lebanese leaders, and others, he was concerned that there was no agreement among them on the tribunal. It was therefore “necessary” for the council to “take the necessary action,” he said.

Mr. Khalilzad said a proposed resolution on the tribunal could be circulated to council members before the end of the week. The risk of internal Lebanese violence once the tribunal is established “has to be compared to the risk of not doing it,” he said. “For reasons of justice, for reasons of long-term stability of Lebanon, and the fact that the Lebanese have requested our help, we need to move expeditiously.”

In a letter to Mr. Ban on Monday, Mr. Siniora requested that the Security Council intervene, saying the internal political situation was impeding the ratification of last year’s council resolution that established the tribunal of international and Lebanese jurists. His government has voted in favor of the tribunal, he wrote, and most legislators have signed a letter to Mr. Ban in support of it. The pro-Syrian opposition, however, has prevented a parliamentary vote. In Israel yesterday, public pressure increased on leaders to act against the Kassam rocket attacks from Gaza. Officials in the town of Sderot, which has suffered the most damage in such attacks, said schools would be closed today in preparation for further attacks.

Mr. Olmert’s Cabinet convened a special meeting that lasted into the night. Several intelligence officials, according to press reports, said the escalation in violence was designed to deflect attention from the infighting in Gaza. “We will not get involved in an internal Palestinian power struggle,” Mr. Peretz reportedly said. But he added that Israel “will respond severely” to attacks on its soil.

Gaza was reportedly quiet last night after a day of internal fighting. Supporters of Hamas fought Fatah-affiliated troops, and large clans struggled to gain the upper hand in an increasingly chaotic struggle for control. Although Prime Minister Haniyah of Hamas announced last night that he had brokered a new cease-fire, Israeli and Palestinian Arab officials expressed skepticism that such an agreement would last.