(Adds deaths and updates details)
SANAA, Feb 13 (Reuters) - Seven people were killed when attackers mounted a bomb, grenade and gun assault on the main prison in Yemen's capital on Thursday in a failed attempt to free inmates, authorities and witnesses said.
Explosions and gunfire between security forces and the attackers could be heard several kilometres away from the prison in northern Sanaa, which has al Qaeda members among its inmates. The biggest explosion rattled windows in the area.
"A terrorist group attacked the central prison," the ministry said in a statement published by state news agency SANA, adding that there was a car bomb followed by a gun attack on the facility.
Seven people were "martyred" and two wounded, it said, using language which suggested the casualties were guards or civilians. Several inmates escaped in the chaos.
"Guards managed to confront the terrorists and forced them to flee," the statement said.
No one claimed responsibility for the attack, but Yemen is grappling with a growing threat from one of al Qaeda's most active wings, which has killed hundreds of people in assaults on state and military facilities in the past two years.
Police sealed off the road to the airport which runs through the neighbourhood where the prison is located.
Earlier on Thursday, a British teacher was reported missing in Sanaa in what a Yemeni security source suggested could have been a kidnapping. The abduction of foreigners in Yemen is common.
The U.S. ally, with a population of 25 million, is trying to end nearly three years of political unrest, which began when mass protests erupted in 2011 against Ali Abdullah Saleh, the president of 33 years, who stepped down.
Interim President Abd-Rabbu Mansour Hadi has been facing other challenges in trying to restore stability to Yemen, which shares a long and porous border with top world oil exporter, Saudi Arabia.
Apart from security, Yemen is trying to deal with demands by southern separatists for independence and incorporate rebels from the Shi'ite Muslim Houthi movement, which has been on an offensive to extend its control over the north. (Reporting by Khaled Abdullah; Writing by Sylvia Westall; Editing by Andrew Roche)
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