A Shiite gunman from the Amal group guards an intersection in a newly seized neighborhood Friday in Beirut, Lebanon. Shiite Hezbollah gunmen seized control of neighborhoods in the Lebanese capital's Muslim sector Friday.

Washington ? On the eve of his trip to the Middle East next week, President Bush faces the collapse of one of his three top priorities in the region – stabilizing Lebanon, a rare Arab democracy – amid new fighting that once again pits the United States against Iran and Syria through surrogates, according to Lebanese and U.S. analysts.

Secretary of State Condoleezza Rice asserted Friday that Hezbollah was not acting alone when its gunmen took over West Beirut on Friday. “Backed by Syria and Iran, Hezbollah and its allies are killing and injuring fellow citizens, undermining the legitimate authority of the Lebanese government and the institutions of the Lebanese state,” she said in a statement.

A senior State Department official said Hezbollah was unlikely to have taken such a brazen step without “some kind of green light” from Iran, given the political and military risks involved. The official also said the appearance of Syria’s Lebanese allies for the first time on the streets of Beirut on Friday to support Hezbollah, after initially staying out of the confrontation, indicates that Damascus is now “pretty heavily involved.”

The Bush administration has been scrambling to mobilize international support for the beleaguered government of Prime Minister Fouad Siniora. Rice spoke to Siniora as well as U.N. Secretary General Ban Ki-moon and the French and Saudi foreign ministers. The Arab League announced an emergency meeting Sunday to discuss the crisis, with the State Department calling on the regional body to show its displeasure with Hezbollah and its sponsors.

The Bush administration has spent $1.3 billion over the past two years to prop up Siniora’s government, with about $400 million dedicated to boosting Lebanon’s security forces. But the assistance has been put in check by Hezbollah – the Shiite militia trained, armed and financed by Iran and Syria – which has the Siniora government under virtual siege.

Lebanon has been central to the administration’s Middle East agenda, especially in promoting democracy. Bush had been scheduled to meet with Siniora in Cairo at the end of his Middle East tour, but it is now unclear whether Siniora will be able to leave Beirut. The airport and port are closed.