The fighting was largely contained to the northern city of Tripoli, where pro-government Sunnis battled members of a Shia sect allied with Hezbollah, with both sides using mortars and heavy machine guns. At least one person was killed there, bringing the death toll since fighting erupted on May 7 to 81. Another 250 people have been injured, making it the worst civil violence since the country's 1975-1990 civil war. Fighting continued in the city on TUESday.

With the country's airport closed, throngs of people continued to flee overland to Syria. Another 200 left by ferry to Cyprus, while others were reportedly escaping by sea in private boats.

In a move some hoped might help bring an end to the fighting, Lebanon's army last night announced that starting today it would use force if necessary to bring an end to the clashes. The military, which has members from all of Lebanon's myriad factions, has remained neutral thus far in the conflict.

"Army units will halt violations ... in accordance with the law, even if that leads to the use of force," the army said in a statement.

The battles thus far have been lopsided, with the opposition seizing control of predominantly Sunni West Beirut, then defeating pro-government fighters from the secretive Druze sect in Mount Lebanon, southeast of the capital. In both cases, the opposition forced the surrender of pro-government fighters, and then handed control of the newly won territory over to the army.

But Ali Hamdan, a senior figure in the Amal movement that has been fighting alongside its fellow Shiites in Hezbollah, said that the opposition's aims have not been achieved since Mr. Siniora's government has not yet formally rescinded two cabinet decrees that sparked the current conflict.

The fighting erupted last week shortly after the cabinet announced a crackdown on Hezbollah's private communications system, a step Hezbollah leader Hassan Nasrallah likened to a "declaration of war." The government also fired a Shia brigadier-general from his post as head of airport security, accusing him of spying on airport traffic for Hezbollah and its backers in Iran and Syria.

Though Lebanon's army intervened to overturn the two decrees, Mr. Siniora has not yet revoked them on paper, said Mr. Hamdan, who is an aide to Amal leader Nabih Berri. In an interview, Mr. Hamdan said the government had consistently underestimated how far the opposition would go to achieve its aims.

"Our reaction [to the decrees] was not to send a message. It was to change and correct something wrong that happened. They'd better do it. For everybody. For Lebanon and the Lebanese," he said shortly after he and Mr. Berri received Michele Sison, an envoy from the U.S. embassy who was shuttling between the various factions yesterday. The U.S. does not speak to Hezbollah, calling it a "terrorist" organization.

Hezbollah warned yesterday that any hint of U.S. intervention in the current crisis could result in unrestrained warfare against the Western-backed government.

Lebanon has been in deep political crisis for almost 18 months, and without a president since November, when Emile Lahoud stepped down. Parliament was to convene today for what would have been the 19th attempt to elect a successor, but that was again posted until June 10.

Both sides support the election of army chief Michel Suleiman as president, although the opposition is holding up the vote, demanding it be given enough cabinet seats to hold a veto over all government decisions.

Mr. Siniora's allies remained defiant yesterday, with former president Amin Gemayel saying Hezbollah could not achieve its aims militarily. "If they want to kill us in our homes, they can go ahead, we have our children and our grandchildren who will continue to fight for the country's independence, sovereignty and honour," he said.

An Arab League delegation is expected to arrive in Beirut tomorrow in an attempt to mediate between the two sides.

Simon Karam, a former Lebanese ambassador to the United States, said most of the country is now effectively under the "direct rule of Iran," something Mr. Siniora and his allies in the West would have little choice but to get used to.

"Do you expect any reaction beyond the promenade of the USS Cole?" he asked rhetorically. "They will accept the fait accompli."

Canadian Foreign Minister Maxime Bernier yesterday blamed Hezbollah for the continuing unrest, adding that "we are supporting the Lebanese government and we hope that peace and security will come back to Lebanon."