Insurgents killed four members of Iraq's security forces and a city engineer in separate incidents across the Iraqi capital Sunday evening, officials said.

The similar nature of the attacks — all were shootings by assailants armed with silencers — and the fact that they all occurred within less than an hour of each other suggested a coordinated campaign to target security officials and government workers. There was no immediate claim of responsibility.

Iraqi police and hospital officials said gunmen killed an off-duty traffic policeman in a drive-by shooting in eastern Baghdad around 8 p.m., and shot dead an Iraqi army colonel in his car downtown.

Assailants killed two more policemen in separate incidents later Sunday in Baghdad, as well as a city engineer northeast of the capital.

Gunmen also targeted a police colonel driving in northern Baghdad, but he escaped with severe wounds and was taken to the hospital.

Insurgents in Iraq frequently target the country's security forces and government employees for a variety of reasons, including retribution or to intimidate others from joining the security services.