MANILA -- Fighting intensified in the embattled southern Philippine city of Zamboanga on Saturday as hopes for a quick cease-fire with Muslim rebels evaporated amid some of the most serious violence to strike the troubled region in years.
The six-day standoff with the rebels in Zamboanga, one of the most vibrant trading cities in the southern Philippines, is believed to have left at least 55 people dead. It has also raised fears of a setback in the government's efforts, backed by the United States, to calm insurgencies and fight terrorism.
The government says most of the dead are rebels fighting government troops. The forces are firing mortar rounds and battling street by street to take back several seaside neighborhoods from the militants.
The situation is serious enough that the country's top civilian and military leaders have traveled to the city, despite the mayhem, to plan their strategy. President Benigno S. Aquino III arrived Friday, with one of his escort helicopters taking small-arms fire as he landed, to coordinate the government's response. The crisis has crippled the once peaceful city, a mostly Christian enclave on Mindanao island, displacing more than 62,000 people.
There are conflicting reports about how the standoff began Monday morning. The police say several hundred armed men from the Moro National Liberation Front landed by boat in Zamboanga and tried to raise their flag over City Hall and declare independence from the national government. When police officers and the military tried to stop them, the police said, the insurgents took hostages and retreated to the city's Muslim slums.
Rebel leaders have said that their march to City Hall was peaceful, and that they were attacked by the military.
Since then, government officials say they have worked hard to evacuate civilians in the area, but it remains unclear how many hostages are being held.
Hopes for a cease-fire briefly emerged Saturday when the vice president -- a political rival of Mr. Aquino's -- announced an informal truce with the rebels. But the fighting never let up, and the president's aides have since said that the administration will coordinate the military actions and any efforts to engage the rebels in talks. At a televised news conference on Saturday afternoon, the government did not answer questions about whether it was trying to negotiate with the militants.
The violence comes less than a year after Mr. Aquino achieved relative peace in the region by winning a deal with a much larger rebel group, the Moro Islamic Liberation Front. The various insurgencies in the region are driven in good part by beliefs by Muslims that they are left out of economic development by the Christian-dominated national government.
On Saturday, Zamboanga's mayor, Beng Climaco, said in an emotional statement during an afternoon news conference that she had turned over management of the crisis to national officials.
"The spate of events that unfolded and continue to unfold are very heartbreaking and upsetting," she said.
In addition to Mr. Aquino, attendees at Saturday's strategy planning session included Vice President Jejomar Binay; the secretary of national defense, Voltaire Gazmin; and Interior Secretary Mar Roxas.
Mr. Roxas told reporters after the meeting that the military's plan had been to contain the rebels to the affected neighborhoods and prevent the violence from spreading to other parts of the city. That has been accomplished, he said, and though he declined to offer details, he said the military was now trying to clear the rebels out of the neighborhoods they were holding.
As of Saturday afternoon, three civilians had been killed in the fighting and 28 had been wounded, officials said. In addition, three police officers had been killed and 11 had been wounded, while two members of the military had been killed and 38 had been wounded.
Mr. Roxas said that the bodies of 21 rebels had been recovered, and that 26 others had also been reported killed. Some of the bodies, he said, were burned in fires that the government says were set by the rebels. Military officials estimate that about 100 rebels remain in the area.
More than 400 homes in the rebel-held areas have been burned, and major sections of the city are impassable. The airport has been closed for five days, and commercial ships have been asked to move away from the port area for security reasons.
"The entire city is virtually isolated from the world," said Ms. Climaco, the mayor. "Innocent lives have been lost, properties have been damaged and our economy paralyzed."
The Moro National Liberation Front signed a peace deal with the Philippine government in 1996, but many of its members retained their weapons. Leaders of the group have said that a peace deal last year with a rival group, the Moro Islamic Liberation Front, has undercut their own peace agreement.
This article originally appeared in The New York Times.