UNITED NATIONS — As Lebanon’s army yesterday intensified its fight against militants ensconced in a Palestinian Arab camp in the northern part of the country, international attention was focused on other Palestinian Arab organizations as possible perpetrators of an attack against Israel on Sunday.

Secretary-General Ban and the Security Council yesterday denounced the rocket attack on Kiryat Shemona, a town near Israel’s border with Lebanon, as did Prime Minister Siniora of Lebanon. Even Hezbollah reportedly said it planned to investigate the attack.

The cross-border incident on Sunday and the prolonged war waged by the Lebanese army in Palestinian Arab camps appear to be part of a pattern of unrest that includes an increased number of political assassinations in Lebanon. The violence underlines the fragility of Beirut’s pro-Western and pro-democracy government, which faces a similar pattern of threats as governments in Iraq, the Palestinian Arab territories, and elsewhere across the Arab world.

Three Lebanese Army soldiers were killed in fighting at the Nahr al-Bared refugee camp near Tripoli yesterday. The camp has been surrounded since May 20, when armed men belonging to Fatah Al-Islam, a group reportedly affiliated with Al Qaeda, holed up there. The Lebanese army has intensified its bombardment of the camp, where 72 soldiers, at least 60 Fatah Al Islam militants, and more than 20 civilians have already been killed.

According to a report delivered to the Security Council by a U.N. envoy to Lebanon, Terje Roed Larsen, Fatah Al Islam is only one of several organizations active in Palestinian Arab refugee camps in Lebanon, where the flow of arms across the border with Syria presents a renewed challenge for the government and violates the council’s resolutions. Those organizations, including the Popular Front for the Liberation of Palestine-General Command and Fatah-Intifada, Mr. Larsen noted, are headquartered in Damascus.

Skirmishes erupted last week at a camp at Ayn Al Hilwa, near Sidon in southern Lebanon, in which two Lebanese army soldiers were killed. A large explosion was heard there yesterday, a device detonation that appeared to be accidental. The group that launched Katyusha rockets against Kiryat Shemona on Sunday was based in that camp, according to some press reports in Israel — although the launches apparently took place near the town of Addaisseh near the border with Israel.

An unnamed official of the U.N. Interim Force in Lebanon was quoted yesterday as saying that Hezbollah, the illegally armed Shiite group controlling most of southern Lebanon, has launched an internal investigation into the Katyusha launches, apparently fearing Israeli retaliation.

On Sunday, Prime Minister Olmert told Mr. Ban that Israel intends no such retaliation. But according to an official who participated in the meeting, Mr. Olmert added that the response might have been different had there been Israeli casualties in Kiryat Shemona.

A unanimous Security Council yesterday “strongly condemned” Sunday’s attack, describing it as a “serious breach” of the resolution that ended last summer’s war. The council also approved a request by Mr. Siniora to add last week’s assassination of an anti- Syrian Lebanese politician, Walid Eido, to a list of political assassinations under a U.N. investigation launched after the February 2005 killing of a former prime minister of Lebanon, Rafik Hariri.