Dhiab Hamad al-Hamdani and his son, Munah, were shot in the oil city of Kirkuk, north of Baghdad, police Colonel Shirzad Mofari said.
They were the uncle and nephew of Khidr Hasan al-Hamdani, a leader of the Patriotic Union of Kurdistan (PUK), one of two main Kurdish parties in the city that is also home to Sunni Arab and Turkmen populations.
An interior ministry source said armed men killed Ali Karim al-Asadi, a Shia member of the Badr Organisation, the former military wing of the Supreme Council of the Islamic Revolution, in Baghdad.
Mushrif Ibrahim Khalil, a retired air force general, was shot dead in Saidiya, south of the capital, while driving in his car, the source said.
The US army said a marine serving at a forward base near Falluja died on Friday of a "non-hostile shotgun wound" in al-Anbar province.
According to the last update of a Pentagon website, 2156 US military personnel have been killed in Iraq since the US-led invasion in March 2003.