Twelve Iraqi police officers have been arrested in connection with a string of kidnappings and killings, including the killing of the sister of one of Iraq's vice presidents, a spokesman for the Interior Ministry said Monday. The announcement came as sporadic violence continued across Iraq, including the deaths of three American soldiers and their interpreter who, the military said in a statement, died in combat operations in Diyala Province in the east. The military did not release further details. In the arrests of the police officers, the suspects, who all were low-level officers, admitted involvement in the killing of Maysoon al-Hashemi, the sister of Tariq al-Hashemi, one of Iraq's two vice presidents, said Maj. Gen. Abdul Karim Khalaf, the Interior Ministry spokesman. Ms. Hashemi, who was director of women's affairs for her brother's party, the Iraqi Islamic Party, was shot to death in 2006.