Fierce clashes are raging in Beirut after the Iranian-backed Hizbullah said the US supported Lebanese government had declared war by targeting its communications network.
Fighters from Hizbollah and the allied Amal group exchanged assault rifle fire and rocket-propelled grenades with pro-government gunmen in several areas of the capital in the worst domestic fighting since the 1975-90 civil war.
Security sources said at least one person was killed and eight were wounded in the fighting that also set several shops and cars on fire.
Supporters of Hizbullah and its allies blocked roads leading to the airport - Lebanon's only air link to the outside world - and other main streets, paralysing much of the city. Middle East Airlines, the national carrier, has suspended departures.
Hizbollah has led a political campaign for almost 18 months against Prime Minister Fouad Siniora's anti-Syrian cabinet.
Meanwhile, the White House has demanded that the group stop its "disruptive activities."
"Hizbollah needs to make a choice: be a terrorist organization or be a political part, but quit trying to be both," said White House spokesman Gordon Johndroe
"They need to start playing a constructive role and stop their disruptive activities now," he said.
Presiden Bush will meet Lebanese Prime Minister Fouad Siniora on May 18 in Egypt at the end of a week-long visit to the Middle East.
