The calls began at 2:55 a.m. on May 20 when Lebanese security forces surrounded a Tripoli apartment building used as a safe house by Fatah al Islam, a newly formed militant group with Qaeda aspirations.

“Stop it or I will go out and attack,” the group’s military commander, Abu Hureira, said from his headquarters in the Palestinian refugee camp Nahr al Bared, north of Tripoli, according to a recording of the conversations that was played for reporters with The New York Times.

A sheik acting as an intermediary relayed the warning to Maj. Gen. Achraf Rifi, head of Lebanon’s Internal Security Forces, who replied, “You will surrender and go to prison, or you will die.”

Seconds later, General Rifi’s men stormed the safe house, killing 12 suspected militants. In response, Fatah al Islam rushed an army checkpoint at the camp’s entrance, killing 23 soldiers sleeping in tents. The continuing battle, which has claimed more than 200 lives, has ruined the camp, now the scene of daily artillery barrages as the Lebanese Army tries to flush out Fatah al Islam.

The fight has drawn scrutiny here and abroad because the militants are foreigners and veterans of the war in Iraq. As Lebanon falls increasingly into a state of political paralysis, the risk of militants setting up base here is raising alarms, especially among European intelligence officials.

One year ago, this country found itself in the middle of a war between Israel and the Lebanese militia Hezbollah after Hezbollah fighters crossed the border and seized two Israeli soldiers. Although the war’s catastrophic damage drew Lebanese together, they quickly turned on one another politically. Killings, bombings and political protests have become routine.

Political forces find themselves stalemated, with no one firmly in charge. Neighborhoods of rubble from last year’s war remain uncleared, and politicians on each side accuse those on the other of blocking reconstruction to prevent them from getting credit.

Parliament has to select a new president in September, but with the governing coalition and the opposition hostile to each other, that could set off an unraveling of what remains of the system of governance.

“If you are in a hole, at least stop digging,” said Ali Hamdan, foreign affairs adviser to Nabih Berri, speaker of Parliament, leader of the Shiite Amal movement and a close ally of Hezbollah. “Unfortunately, the Lebanese keep digging.”

While Lebanon’s troubles are not principally about Islamic militancy, some fear it could become the kind of place that attracts more of it, especially from the Iraq war.

General Rifi, the internal security chief, estimates that 50 to 60 fighters are still in the camp and they include skilled and determined militants from Saudi Arabia, Syria, Yemen and Algeria who fought with the insurgency in Iraq.

The group’s leader, Shakir al-Abssi, was an associate of Abu Musab al-Zarqawi, the leader of Al Qaeda in Mesopotamia killed last summer. He has been sentenced to death in Jordan for helping Mr. Zarqawi organize the 2002 slaying of an American diplomat in Amman, Jordan.

“One reason we attacked Abssi was to get a message to those people that you don’t have to come to Lebanon after your mission in Iraq,” General Rifi said.

But Mr. Abssi has been drawing support from Europe as well, according to a Western European intelligence official who spoke on condition of anonymity. There is some evidence that Islamic militants in Western European countries traveled to Lebanon and joined Mr. Abssi’s group, the official said, citing recent reports from intelligence agencies of countries other than Lebanon.

Meanwhile, Lebanon has been hit with a rash of car bombings and other violence since the fighting with Fatah al Islam began, including a car bomb in the south that killed six United Nations peacekeepers.

Today, the Lebanese are increasingly divided by rolls of razor wire spread across roads and wrapped around buildings and homes. They are separated by military checkpoints that tie up traffic. Nearly a dozen members of Parliament have left the country, fearful they will be killed. Some United Nations officials have moved from their heavily guarded offices in the center of Beirut to smaller, less obvious space deep behind a sea of razor wire.

Given Lebanon’s fractured politics — and the backing of Hezbollah by both Iran and Syria and of the government by Western powers — it is too soon to know who has been behind the many incidents. General Rifi said the F.B.I. director, Robert Mueller, paid him a surprise visit last week and offered forensic assistance in analyzing the bombings.