Hussein Malla, Associated Press
Passengers head toward Beirut's international airport terminal on Thursday as fires, set in the streets by Hezbollah gunmen, burn behind them.

BEIRUT, Lebanon — Fierce clashes escalated in Beirut on Thursday between Sunni supporters of the government and loyalists of Hezbollah, the Shiite militant group, after Hezbollah's leader said the government had declared war by threatening to shut down the group's private telephone network.

The fighting was the worst since Lebanon's 15-year civil war, which ended in 1990. At least four people died and seven others were wounded, according to security officials. The comments by Sheik Hassan Nasrallah, the leader of Hezbollah, were the strongest since Lebanon's political crisis began 17 months ago. The developments could signal a new level of confrontation between Hezbollah, which is supported by Iran and Syria, and the government of Prime Minister Fouad Siniora, which is backed by the West and Saudi Arabia.

The standoff has left the country without a president since November.

Nasrallah left open the door for negotiations by saying that Hezbollah would back down if the Sunni forces left the streets of Beirut and the government reversed its decision to try to shut down the telephone network.

After Nasrallah's speech, the leader of the largest bloc in parliament, Saad Hariri, a Sunni, proposed a deal to end the fighting and called the government's decision on the telephone network a misunderstanding.

Later on Thursday night, Al Manar television, which is run by Hezbollah, said the group had rejected Hariri's proposal. The station cited a pro-Hezbollah official, who said the group and its allies would reject any ideas for ending the conflict that were not proposed by Nasrallah.

"My appeal to you and to myself as well, the appeal of all Lebanon, is to stop the slide towards civil war, to stop the language of arms and lawlessness," Hariri said.

Nasrallah, speaking at a news conference via a video link, said the telephone network, which connects Hezbollah's officials, military commanders and emplacements, was a vital part of the group's military infrastructure.

By late Thursday, masked gunmen were roaming the streets with walkie-talkies. Some were seen shooting out streetlights to keep rooftop snipers from directing their fire at targets.

Many residents along Corniche Mazraa, a major highway that has become a demarcation line between the factions, were seen leaving their houses for safer areas. Others lined up in supermarkets, stocking up on food supplies. -->

Several parts of the city were shut down, and roads were blocked by burning tires and garbage cans set on fire.

Fighting also broke out in the Bekaa Valley, to the east.