Unidentified gunmen on Saturday attacked the central prison in Niger's capital, opening fire on the guards and killing at least two people, according to a government spokesman and a witness who was 200 meters (yards) from the prison when the incident occurred. It was not immediately clear if the assailants had come from inside or outside the jail, ABC News reported. Two security guards were killed and a third was gravely wounded, said Niger government spokesman Marou Amadou. He said the attackers had been captured and the incident is being investigated. "There are two versions of what happened, and right now we think it's more likely that they came from inside the jail," Amadou added by telephone. "These are people who are wanted for terrorism. We do not know how they were able to arm themselves inside the prison, and how they were able to get out attacking the guards. We have two dead guards already and one seriously wounded," he said.