Afghanistan has barred two private security firms from one of the country's most dangerous highways after their guards shot and killed two civilians, the government said Sunday...The victims were killed accidentally in separate incidents...interior ministry spokesman Zemarai Bashary said both companies had also been ordered to pay compensation to the victims' families. "The perpetrators of both incidents have been arrested and are being prosecuted," he told journalists at a press conference in Kabul following the killings, which both occurred in the last two weeks...The two firms, Compass and Watan Risk Management, are among 52 private security companies registered to operate in Afghanistan...