The Al Qaeda terrorist organization has taken over the south central Yemeni town of Zinjibar, the capital of the Abyan province.

A resident in the town told a Reuters news reporter Sunday, “About 300 Islamic militants and Al Qaeda men came into Zinjibar and took over everything on Friday.”

Sporadic fighting was continuing on Sunday between Al Qaeda gunmen and the besieged 25th mechanized brigade, according to an AFP journalist who reached an officer from the brigade's headquarters. The security officer told him by telephone, “We will fight until the last bullet, and we will not surrender to the gunmen who killed our companions.”

Witnesses reported that terrorists executed soldiers who surrendered, and residents were not able to bury them. Dozens of families fled to Aden, further south. One man, Nazir Ahmed Said, told AFP he left because “the city is under the control of gunmen who say they are from Al Qaeda.”

At least 16 people were killed in the fighting, which was reported heavy throughout Friday and Saturday. The attackers freed dozens of prisoners from the main jail in Zinjibar, residents said.

The terrorist invasion took place against the backdrop of a worsening civil war that last week alone claimed the lives of at least 124 people and injured hundreds more.

President Ali Abdullah Saleh has spent the past three months fighting to maintain his 33-year-old grip on the nation's government, but it is proving to be a losing battle, despite his warning that if his regime were to fall, Al Qaeda would be the benefactor.

In the past, Saleh has been a key U.S. ally in the fight against the terrorist organization's local branch, Al Qaeda in the Arabian Peninsula.

But in a recent effort to quell the rising tide of protests across the country, government forces killed some 150 demonstrators, further alienating the diminishing number of Saleh's supporters.

On Sunday, an entire brigade of the president's powerful Republican Guard, which is controlled by Saleh's son, reportedly defected to the opposition forces. A letter from Brigadier-General Ibrahim al-Jayfi, commander of the Guard's Ninth Brigade, was read to thousands of protesters in the capital of Damar, announcing the news.

It was the first reported defection among the elite forces, according to the Associated Press.

Last week Saleh's forces attacked the home of Sheikh Sadeq al-Ahmar, once a strong tribal ally but more recently an opponent who had joined the rebel forces. Ahmar heads the powerful Hashid tribal confederation, which immediately came to his defense, seizing government buildings in the process.

Fighting soon spread, with tribal leaders also seizing two army posts north of the capital, Sana'a, on Friday.

By Saturday, the two sides had begun to negotiate, and an agreement was reached late in the day for each to withdraw their forces on Sunday morning.

Within hours, the two sides were abrogating the agreement. Government forces had issued an arrest warrant for Ahmar, and tribal leaders were urging security forces to desert the president -- who has several times negotiated an agreement to end his rule and transfer power, but then backed away from signing the deal with representatives sent by the opposition.