Gunmen in western Ethiopia killed at least 34 people in an attack on a bus on Saturday night, the national human rights body said on Sunday, as fears grow of a security vacuum in the country amid a military campaign in the north. The Ethiopian Human Rights Commission said the number of people killed was likely to rise after what it called a “gruesome” attack on the passenger bus in the Benishangul-Gumuz region. “The latest attack is a grim addition to the human cost which we bear collectively,” Daniel Bekele, commission head, said in a statement.