Angola’s UNITA rebels said they killed 193 government troops last week. They said this included the toll taken in the ambush of a military column in which 68 government soldiers and 11 Cuban advisers were slain. The National Union for the Total Independence of Angola said the Marxist government has stepped up a dry-season offensive in the nation’s southeast. But Angolan authorities deny any new offensive, passing it off as an invention by UNITA to ensure continuing U.S. aid. The New York Times quoted Western diplomats as saying a secret airlift of U.S. arms to the guerrillas is continuing via southern Zaire.