UNITED NATIONS — Lebanon is on the brink of war, according to American and U.N. officials, with the leader of Hezbollah threatening to “cut off the hand” of his Lebanese enemies and their Western allies, and armed factions facing off on the streets of Beirut.

At least three people were killed in clashes in the Lebanese capital yesterday, according to wire reports. The tense situation has followed initial attempts by the Lebanese army, controlled by the Western-supported Prime Minister Siniora’s government, to confront Hezbollah, which is armed and supported by Iran and Syria and has become a “state within a state,” Western diplomats said.

With more and more factions arming around the country, and as a political impasse has prevented parliament from convening to elect a new president since last November, Hezbollah has increasingly acquired all the trappings of a state within a state, Western officials said yesterday. Secretary-General Ban’s Lebanon envoy, Terje Roed Larsen, said Syria and Iran have “close ties” with Hezbollah and accused the two countries of playing “negative role” in Lebanon’s political impasse, undermining the government’s ability to assert its authority over the entire country.

But the top Hezbollah leader, Sheik Hassan Nasrallah, said that Prime Minister Siniora’s government is “in the camp” of the Shiite group’s enemies. Anyone who tries to disarm Hezbollah is acting “for the benefit of America and Israel,” he said, according to several wire services. “We believe the war has started, and we believe that we have the right to defend ourselves,” he added. “We will cut the hand that will reach out to the weapons of the resistance, no matter if it comes from the inside or the outside.”

In a report to the Security Council, Mr. Ban wrote that as Hezbollah remains armed, other militias in the country rush to obtain weapons as well. The situation has become increasingly tense, and riots earlier this week “show tragically that the country today confronts challenges of a magnitude unseen since the end of the civil war” in Lebanon in the 1980s, Mr. Roed Larsen told the Security Council yesterday.

“Lebanon is once again on the brink,” the American ambassador to the United Nations, Zalmay Khalilzad, said. “Hezbollah and its allies are challenging the government. They have established and made progress in establishing a state within a state. They have not implemented agreements and resolutions with regard to disarming their militia. That, in turn, is encouraging other groups to rearm as well.”

Mr. Roed Larsen called on Damascus to abide by a call made by the Security Council, and during a meeting of Arab and Western countries in Kuwait last month, to establish diplomatic relations between Syria and Lebanon and delineate the borders between the two countries. Critics have accused Syria of interfering with Lebanon’s politics in order to seat a puppet regime that would allow it to regain its control of the country.

But Syria accused Mr. Larsen of promoting his “own agenda” on behalf of Israel and America. Syria has “no problem in principle” with establishing diplomatic relations with Lebanon, the Syrian ambassador at the United Nations, Bashar Jaafari, told The New York Sun yesterday. But “that should be done once we have a friendly government in Beirut,” he said.

In yesterday’s council briefing on the fast-paced deterioration of Lebanon, Mr. Roed Larsen detailed several events that occurred in recent weeks, urging a negotiated solution, but saying that the country “for a long time has been on the slippery slope.” Hezbollah has built its own secure communication network, separate from the state system that covers many parts of the country, he said. The network “connects to a Syrian network beyond the border,” he said.

He quoted Lebanese government sources as saying that Hezbollah has established its own system of surveillance cameras in the Beirut airport. That discovery led to the removal of the pro-Hezbollah General Wafiq Shoucair from his post as commander of security of the airport. Last month, a French delegate to a Socialist International meeting in Beirut was detained by Hezbollah operatives for questioning for more than five hours in South Beirut, for what Hezbollah said was “security concerns,” Mr. Roed Larsen reported.

Hezbollah, “the most significant Lebanese militia, maintains a massive paramilitary infrastructure,” Mr. Roed Larsen told the council. “This has an adverse effect on the efforts of the government of Lebanon to enjoy the monopoly on the use of force and impose law and order in the country.”

The top Republican on the U.S. House of Representatives’ Foreign Affairs Committee, Rep. Ileana Ros-Lehtinen, yesterday called for “punitive action” against Iran and Syria for their role in Lebanon. “The Iranian and Syrian regimes are complicit in this violence by arming Hezbollah, a group responsible for shedding the blood of innocent Lebanese dissidents and political leaders,” she said. “The regimes in Damascus and Tehran continue to kill, attack, destroy, and sow discord in Lebanon, Iraq, and elsewhere, only to then offer themselves as the solution, so that they may gain yet more power and influence in the region.”