More than 60 suspected al-Qaeda militants escaped from a jail in southern Yemen on Wednesday through a tunnel, authorities said, the latest sign that insurgents are capitalizing on the political unrest that has rocked the country for months.

The inmates dug the 50-yard-long tunnel themselves, said one official at the jail, who spoke on condition of anonymity because he was not authorized to give details of the escape.

They attacked a guard with daggers, snatched his gun and fired it as they were making their escape, the official told The Washington Post. One guard was fatally shot, and another was wounded.

The Associated Press reported that bands of gunmen attacked the prison from the outside just as the prisoners were escaping, opening fire on guards to divert their attention from the escape.

The official told The Post that 57 of the 62 escaped militants had been convicted on terrorism charges, and some had been sentenced to death. Twelve of them were from a particularly dangerous al-Qaeda cell known as the Tarim cell, the official said.

Islamic extremists have been battling government forces for control of southern Yemen, taking advantage of a growing power vacuum that began months ago with mass demonstrations and worsened when President Ali Abdullah Saleh was injured in an attack on his presidential compound June 3.

Saleh was then flown to neighboring Saudi Arabia for medical treatment, and Vice President Abed Rabbo Mansour Hadi was named acting president.

U.S. and Yemeni officials worry that a loss of government control in the south could further destabilize this strategic but desperately poor Middle Eastern nation. Shortages of fuel, food and other essentials are adding to the tension.

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

Wednesday’s escape happened at the jail in Mukalla, a port in the southeastern province of Hadramut. Hadramut is the biggest province in Yemen and the source of much of Yemen’s oil.

The escape coincided with a visit to Yemen by Jeffrey D. Feltman, the U.S. assistant secretary of state for Near Eastern affairs. Feltman met with Hadi on Wednesday and praised the acting president’s efforts to maintain a cease-fire with armed factions supporting the political opposition, according to Yemen’s state-run news agency. It said Feltman also welcomed Hadi’s moves to open roads, remove armed men from cities and meet with political opponents and youth movement activists.

Hadi told Feltman he appreciated President Obama’s efforts to defuse tensions in Yemen, the agency said.

However, a leading opposition group, the Organizing Committee of the Popular Youth Revolution, issued a statement denouncing Feltman’s visit and calling on anti-government activists to boycott it.

Wilgoren reported from Washington. Correspondent Sudarsan Raghavan also contributed to this report.