* Infiltration raises concerns in oil-rich region
* Yemeni source says Yemen and Oman cooperating (Recasts with al Qaeda members fleeing prison)
SANAA, June 26 (Reuters) - Up to five al Qaeda members escaped a Yemeni prison on Tuesday as Omani and Yemeni security forces hunted for several other militants fleeing a military offensive in southern Yemen who crossed into Oman, Yemeni security sources said.
The infiltration into Oman, which sits on one side of the Strait of Hormuz, a conduit for one third of the world's seaborne oil exports, fuelled fears that Islamist militants may try to set up a base in a region of strategic importance for the United States.
"A limited number of al Qaeda elements managed to cross the border line to Oman in recent days," the Yemeni source told Reuters. "Both sides are coordinating at the level of the border guards and the intelligence service to pursue and capture them."
An Omani foreign ministry official, Badr bin Hamad al-Busaidi, told the newspaper "Oman" that his country was hunting infiltrators from Yemen, but he said no arrests had been made.
The small oil and gas exporter is an ally of the United States and Britain.
Separately, in the northern Yemeni province of Hodeidah, at least 23 inmates, including a number of al Qaeda operatives, fled prison, a security official told Reuters.
"They dug a tunnel from their cell leading to a nearby grave yard," the official, who asked not to be named, said. Saba state news agency said five militants had fled the prison.
Saudi Arabia fought a militant insurgency from 2003 to 2006 in which al Qaeda members killed dozens of people in attacks on foreign workers and on government facilities.
Many of the militants fled the Saudi crackdown and regrouped to set up a base in Yemen.
Ansar al Sharia, an offshoot of al Qaeda, last year exploited political turmoil to capture several cities in southern Yemen, before being driven out by government forces this month who now appear to have the rebels on the run.
Yemeni officials have said some militants have fled towards a province bordering Oman.
Last year, the sultanate was rocked by mass protests against corruption and unemployment, which appeared to have been inspired by the Arab Spring uprisings.
Those protests have now subsided, largely giving way to sporadic labour protests in the oil, health and education sectors. (Reporting by Sami Aboudi and Mohammed Ghobari in Sanaa; Editing by Kevin Liffey and Andrew Osborn)