BEIRUT (AFP) - - Lebanon was steeped in tension on Saturday after Hezbollah seized control of west Beirut in three days of deadly fighting with pro-government forces, triggering fears of all-out civil war.

At least 16 people were killed in the violence that erupted on Wednesday and quickly escalated after the head of the opposition Shiite Hezbollah movement called a government crackdown on his powerful group a declaration of war.

The unrest led to urgent international appeals for calm as Arab foreign ministers prepared to hold an emergency meeting on the crisis on Sunday amid regional Sunni Muslim fears about Shiite Iran's influence in Lebanon.

The United States said Hezbollah's actions proved it was a threat to the entire region.

"Hezbollah's relationship with Iran and Syria, as well as its history of international terrorism and provision of lethal support and training to Iraqi-based extremist groups, demonstrates the threat it poses to international peace and security," White House spokesman Gordon Johndroe said on Friday.

Analysts said there were fears the violence could spread beyond Lebanon's borders.

"Hezbollah had said before it would never point its arms against its own country, but it has crossed this line," said Nadim Shehadi, Lebanon expert at the Chatham House think tank in London.

"Hezbollah has crossed a huge red line, and it means Iran has crossed this line. The political consequences are immense -- it could escalate regionally."

Antoine Basbous of the Paris-based Observatory of the Arab Countries predicted more violence .

"There will be operations, attacks. It (Hezbollah) will not totally control the new territory (it has seized) because it is not welcome" there, Basbous said.

Hezbollah gunmen celebrated on Friday by firing into the air and flashing victory signs as they drove in convoys around west Beirut after routing Sunni militants loyal to Prime Minister Fuad Siniora's Western-backed government.

The army and police moved into areas now in the hands of Iranian- and Syrian-backed opposition forces which have been locked in an 18-month power struggle with the ruling coalition.

But five people were killed in flare-ups elesewhere across the country on Friday, including a man and his wife in the southern port of Sidon -- a stronghold of ruling majority leader Saad Hariri.

Foreigners scrambled to leave the region via Syria and governments prepared evacuation plans from Lebanon as the country's sole civilian airport and Beirut port were shut and key highways blockaded.

The fighting brought back harrowing memories of the 1975-1990 civil war as Hezbollah and its foes both appeared unwilling to give any ground.

Hezbollah insisted that the roadblocks that have paralysed transport across much of the nation would remain until the government meets its demands.

But Youth and Sports Minister Ahmed Fatfat said the government would not go back on its decision to probe Hezbollah's private communications network -- the trigger for the latest unrest.

Beirut residents cowered inside their homes on Friday after a night rattled by gunfire and exploding rocket-propelled grenades, while most shops remained shuttered.

Christian opposition leader Michel Aoun, a key ally of Hezbollah chief Hassan Nasrallah, hailed Friday's events as a "victory for Lebanon."

But another Christian leader, Samir Geagea, accused Hezbollah of launching "an armed coup."

Hezbollah was the only faction allowed to keep its weapons after the civil war to fight Israeli forces occupying the south.

Lebanon's continuing political feud is widely seen as an extension of the confrontation pitting the United States and its Arab allies and Israel against Syria and Iran.