Four police officers have been shot dead in what is believed to be a targeted attack at a coffee shop near an air force base in Washington state, US. The officers were sitting in the coffee shop before the start of their shifts, reading on their computers, when the shooting occurred, Sheriff's Department spokesman Ed Troyer said. Authorities believe the officers were meeting and going over cases or doing paperwork, he said. A gunman came inside and shot all four officers, Troyer said. Two coffee shop employees and other customers inside the shop were unharmed, said Troyer, who said the shooting "was a targeted, selected ambush."