NAIROBI ? Kenyan President Uhuru Kenyatta replaced two of his top security chiefs after Islamist militants killed at least 64 people in the north of the country in the past two weeks in attacks that targeted non-Muslims. Kenyatta nominated Joseph Ole Nkaissery, a lawmaker for the opposition Orange Democratic Movement, to succeed Interior Secretary Joseph Ole Lenku, he told reporters Tuesday at State House here in the capital. He said he also accepted the retirement of Inspector-General of Police David Kimaiyo. Al-Shabaab, the al-Qaida-linked insurgent group based in Somalia, claimed responsibility for the killing Tuesday of at least 36 people at a quarry in Mandera in northeastern Kenya,...