Islamist extremists, many suspected of links to al-Qaeda, are engaged in an intensifying struggle against government forces for control of southern Yemen, taking advantage of a growing power vacuum to create a stronghold near vital oil-shipping lanes, said residents and Yemeni and U.S. officials.

Over the past few weeks, the militants have swiftly taken over two towns, including Zinjibar, the capital of Abyan province, and surrounding areas and appear to be pushing farther south, said Yemeni security officials and residents. Increasingly, it appears as if al-Qaeda’s regional affiliate is seeking for the first time to grab and hold large swaths of territory, adding a dangerous dimension to Yemen’s crisis.

U.S. and Yemeni officials worry that a loss of government control in the south could further destabilize this strategic Middle Eastern nation, already gripped by political paralysis, violent conflicts and fears of collapse.

The government has not allowed journalists to visit Zinjibar. This article is based on more than a dozen interviews with provincial officials, government employees and tribal leaders from Abyan, as well as Yemeni and U.S. officials, and telephone interviews with residents of Zinjibar and surrounding areas.

They describe a ghost town where streets are a canvas of destruction, struck by daily shelling, air assaults and gunfire. There’s no electricity, water or other services. Tens of thousands, mostly women and children, have fled the city. Men have stayed back only to protect their homes. The extremists man checkpoints, and any semblance of authority or governance has vanished.

“They want to create an Islamic emirate,” said Mohammed al-Shuhairi, 50, a journalist in al-Kowd, near Zinjibar. “I have lived through wars here in 1978, 1986 and 1994. But I have never seen anything as bad as this.”

The Islamist extremists are mostly from various Yemeni provinces but also include other Arabs and foreign fighters. They call themselves Ansar al-Sharia, or Supporters of Islamic Law, residents said.

In an April 18 interview on jihadist Web sites, Abu Zubayr Adel al-Abab, described as a sharia official with al-Qaeda in the Arabian Peninsula, or AQAP, as the Yemen branch is called, said the militants identified themselves as Ansar al-Sharia.

“The name Ansar al-Shariah is what we use to introduce ourselves in areas where we work to tell people about our work and goals, and that we are on the path of Allah,” said Abab, according to a translation by the London-based International Center for the Study of Radicalization and Political Violence.

Growing aggressiveness

The takeover of Zinjibar underscores the growing aggressiveness and confidence of AQAP, which appears to be taking advantage of political turmoil triggered by the populist rebellion seeking to oust President Ali Abdullah Saleh. The crisis has further deepened since Saleh was severely wounded in a June 3 assault on his presidential palace, forcing him to fly to neighboring Saudi Arabia for treatment and raising doubts about his ability to rule.

Long before the death of Osama bin Laden, American officials considered AQAP among the most significant threats to U.S. soil and worried that it could create a launchpad to target the United States and its allies. The capture of Zinjibar and nearby towns gives the group access to the Red Sea and its vital oil shipping lanes. The militants are also well positioned to attack the port city of Aden, about 30 miles south.

U.S. State Department and intelligence officials have worried that AQAP will exploit the worsening security situation in Yemen, and American officials have closely tracked the fighting in Zinjibar as a possible early test of the group’s strength in the region. State Department spokesman Mark Toner said AQAP’s sizable presence puts the country on a different tier compared with other nations hit by political unrest.

“It’s the reason why we’ve had such an ongoing, robust counterterrorism cooperation,” Toner told reporters last week. “But as we’ve said many times, that cooperation isn’t hinged on one individual.” Regardless of who leads Yemen, he said, “we’re going to continue to work with the [current] government” to keep the terrorist group from gaining a foothold.

The rise of the Islamist extremists also complicates a political landscape that is crowded with several groups seeking power, including youth activists, the traditional political opposition, Saleh’s loyalists, powerful tribal leaders and defected military generals.

Although the extremists have not declared any national political aspirations, many fear that they could end up ruling portions of the south in the same way the Houthi rebels have done in the north, further dividing the country and eroding the authority of the central government.

“If they remain, they will have great impact on Yemen’s politics,” said Qassem al-Kasadi, a ruling party lawmaker from Abyan. “They could end up ruling over portions of the south. In the areas they have taken over, they are already manning checkpoints and ordering residents to follow sharia.”

Collapse in authority

Yemen’s rugged south has long provided a hiding place for AQAP militants, who are shielded by sympathetic, anti-regime tribes and impenetrable mountains. One of the group’s top leaders, radical Yemeni American cleric Anwar al-Aulaqi, whom the Obama administration has targeted for assassination, is thought to be in the south.

The New Mexico-born Aulaqi has been implicated in attacks on the United States, including the 2009 Fort Hood, Tex., shootings that killed 13, and the failed Christmas Day attempt that year to bomb a Detroit-bound airliner. Last year, AQAP dispatched parcel bombs on cargo flights to the United States.

It’s unclear how many of the extremists are AQAP members. Thousands of Islamist militants, including many former jihadists who fought in Afghanistan, Iraq and other Muslim nations, live in Yemen. Many have past links to al-Qaeda and express sympathy for the group’s core philosophies. Others have tribal, social and inspirational ties to the terrorist network.

In March, the militants easily seized the small agricultural town of Jaar and surrounding areas, as government troops abandoned their posts. On May 27, extremists took control of Zinjibar, taking advantage of a collapse in authority as government forces battled tribesmen in the streets of Sanaa, the Yemeni capital.

Many of Saleh’s opponents accuse him of intentionally ceding ground as a warning to his allies in the United States and the Arab world, as well as ordinary Yemenis, that the nation would collapse if he were to fall from power. They say he has long exaggerated the threat of AQAP to secure funds and support from the West.

“Al-Qaeda appears whenever the regime wants, and they disappear whenever the regime wants,” said Ahmed Abdullah al-Azani, another lawmaker from Abyan. “If the regime wants, it can easily kick these Islamists out.”

Kasadi said he did not believe that Saleh would allow the Islamists to take over so much territory as a ploy to remain in power. “It’s not in the government’s favor if a province falls,” he said. “That shows part of the government has fallen.”

‘We left everything’

In Zinjibar, residents said government buildings and stores are shut down; many were destroyed by the shelling and airstrikes. Government officials and other sources of authority reportedly have fled.

The militants, mostly bearded youths dressed in civilian clothes, are said to control the streets. They retreat during air assaults, then reemerge when things quiet down. Residents described the extremists as polite and not oppressive. There are as many as 700 militants in Zinjibar and surrounding areas, said Yemeni security officials.

In recent days, as the extremists seek to push farther south, the fighting has intensified. That forced Hussein Nasser Abdullah, 48, on Wednesday to quickly leave his home along with 35 relatives, joining thousands of other families. Some sleep inside public schools in Aden, the rest with relatives and friends. “We left everything back there,” Abdullah lamented.

Ali Ashoor sent his wife and three daughters to another town. He spends his days searching for food and water. By nightfall, he locks himself inside his home and sleeps on the first floor, enveloped in darkness and fear. Saturday night illustrated why.

“I can hear bullets and shelling. Both sides are attacking us,” the 56-year-old retired government employee screamed over his cellphone. “I feel my home will get bombed at any minute.”

“Our future is unknown,” he added moments later.

Staff writer Joby Warrick in Amman, Jordan, and a special correspondent in Sanaa contributed to this report.