Seven Yemeni prison guards were killed and two others wounded as a result of a terrorist attack on the minimum security Central Prison here Thursday afternoon.The gunmen exploded a bomb-laden vehicle before exchanging fire with the prison guards from various locations, the Yemeni Ministry of Interior said in a press release tonight.The security forces returned fire, forced the attackers to fee, cordoned off the area, and started searching the houses believed to be the sources of firing.Some prison inmates managed to take advantage of the chaos and break out, said the statement.A security committee has been formed to investigate the incident, it added.