Beirut, Lebanon ? In the space of just 14 hours, a Shiite militia backed by Iran had seized control of the Sunni heart of an Arab capital.

In a development with profound implications for the future of Lebanon and the Mideast as a whole, the Hezbollah movement routed pro-government Sunni forces in the Muslim western half of Beirut on Friday in intense gun battles that killed a total of 14 people as the Lebanese army declined to intervene.

The U.S.-backed Lebanese government called it a “bloody coup” and showed no sign that it was prepared to compromise on Hezbollah’s demands, despite the defeat of the outgunned and outmaneuvered militia of the Sunni Future Movement, which went into battle for the first time and lost.

Samir Geagea, a Christian spokesman for the March 14 movement that controls the beleaguered Lebanese government, appealed for international assistance in its fight with Hezbollah, which has been demanding that the government step down for the past 18 months.

“The international community cannot remain silent in the face of this subversion,” he said.

U.S. State Department spokesman Sean McCormack pledged “unswerving support” for the Lebanese government and said there was evidence Syria and Iran had played a role in planning the violence.

The standoff between forces loyal to the U.S.-backed government and the Hezbollah-led opposition movement, backed by Iran and Syria, has been building for the past 18 months, but few had foreseen how quickly Sunni domination of West Beirut would collapse.

The Druze leader Walid Jumblatt was besieged in his home, as was the Sunni leader Saad al-Hariri, head of the Sunni Future Movement and son of slain Prime Minister Rafiq Hariri. The Sunni Future television station was forced to stop broadcasting early in the morning and by late afternoon it had been set ablaze.

The Christian eastern sector of the capital remained calm, but with most of the government ministries and institutions in the western sector of the capital, the Hezbollah takeover was deeply symbolic.

The unrest erupted Wednesday, when street demonstrations called by labor unions over the high cost of living turned violent.

More significantly, however, a decision by the government Tuesday to investigate a private communications network maintained by Hezbollah had aroused the Shiite movement’s ire. On Thursday, Hezbollah leader Hassan Nasrallah gave the green light to Hezbollah fighters to take on fellow Lebanese unless the government backed down, and the battle began soon after.

Hezbollah began pushing deep into West Beirut, considered Sunni territory, closing in on the main commercial district in a pincer movement launched from the downtown area to the east and the seafront to the west.

Throughout the night, intense exchanges of deafening gunfire punctuated by the explosions of rocket-propelled-grenades kept residents awake. Gunmen loyal to the Sunni Future Movement, who claimed ascendancy in the neighborhood, darted along alleyways and hid under awnings, battling to hold off the Hezbollah advance. The odor of cordite wafted through the air.

Then, just as suddenly as it had begun, it ended. Dozens of Hezbollah gunmen, some of them masked, marched through the streets, shouting to residents to stay indoors and away from their windows. They were calm, organized and disciplined.

Hezbollah was joined in the fight by the secular Shiite Amal movement and a pro-Syrian faction, the Syrian Social Nationalist Party, whose fighters assumed control of many of the Beirut neighborhoods conquered by Hezbollah as the Islamist fighters pulled back.