Insurgents from the Islamic State (IS) jihadist group killed Sanaa al-Juburi and wounded Khawla al-Juburi in Sharqat, some 300 kilometres northwest of Baghdad, tribal and military sources said.
The motive for the attacks was unclear, but IS espouses a puritanical form of Sunni Islam that severely restricts women's freedoms. It is also fighting against a Shiite-led government that many Sunnis see as sectarian and oppressive.
"The absence of laws, and the rule of law, has led extremists to violate the law as they want," said Shedha Naji of the Women for Peace rights group in Iraq.
IS gunmen killed Sanaa al-Juburi and kidnapped her husband after stopping their car. Gunmen also opened fire on Khawla al-Juburi's home, wounding her and kidnapping her husband.
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The women are not related, but belong to a clan which dominates the area.
IS seized large swathes of northern and western Iraq in a sweeping offensive last month, and is one of an array of Islamist militant groups that have come to prominence in recent years and that take a dim view of women's rights.
Highly conservative Shiite militias have also risen to prominence in many areas, and are known to dispense their brand of summary justice.
Unidentified gunmen using silenced weapons killed 27 alleged prostitutes earlier this month in a residential area of east Baghdad, triggering outrage among women's rights groups.
"Whatever these women were, they have to be dealt with by the law and the guns have to be taken away from anyone not part of state forces," Naji said.
During former Iraqi leader Saddam Hussein's tenure women enjoyed more freedoms and opportunities, and were better educated, women's groups say.
Although rights for women are enshrined in Iraq's constitution, the rise of conservative religion-based political parties after the 2003 US invasion has meant the rules are seldom followed.