(Adds more fugitives, background on other escapes)
ADEN, Dec 12 (Reuters) - At least 16 prisoners, including members of al Qaeda, escaped from a prison in the southern Yemeni city of Aden on Monday, Yemeni officials said.
A security official in the south of the country, where Islamist fighters have seized chunks of an entire province, said detainees fled by digging a tunnel leading beyond the prison's walls. Sixteen were at large, another local official said.
It was the second major jailbreak involving al Qaeda members since June, when dozens of al Qaeda militants escaped from a jail in another city, Mukalla.
Nearly a year of protests demanding the ouster of Yemeni President Ali Abdullah Saleh, punctuated by bouts of fighting between his forces and tribesmen and military units who oppose him, have seen Islamists gain power in the south.
Deteriorating security in the area, where parts of the Abyan province are under control of Islamist fighters, have fanned fears in Saudi Arabia and Washington -- which long backed Saleh in its campaign against al Qaeda -- that the Yemeni branch of the group may gain a foothold near key oil shipping routes.
Al Qaeda members, including one convicted in a 2002 attack on the French-flagged oil tanker Limburg off Yemen, escaped from a jail in the capital Sanaa in 2006, helping to revive the group after Saudi security forces weakened it in that country.
Saleh's foes have accused him of deliberately letting Islamists in the south grow stronger to reinforce his argument that his rule alone can prevent the country sliding into chaos that would empower al Qaeda, whose Yemeni wing has planned abortive attacks on U.S. and other targets.
Reporting by Mohammed Mukhashaf; Joseph Logan