The Islamic State group has executed at least four women, including two doctors and a politician, in their northern Iraq strongholds this month, relatives and rights activists said on Saturday.

In the IS hub of Mosul, the jihadists executed three women on Wednesday including two doctors, Hanaa Edwar, a human rights activist who heads the Al-Amal organisation, said.

A medical source in Mosul confirmed their deaths and named the two doctors as Maha Sabhan and Lamia Ismail. The third woman was a law graduate.

On October 5, Iman Mohammed Yunus, a former Sunni parliamentarian from the Iraq Turkmen Front in the city of Tal Afar, farther west towards the Syrian border, was also executed.

"They took her from her home last month and called her family this week to say that she had been executed," said Ali al-Bayati, who runs a foundation supporting the rights of Iraq's Turkmen minority.

"Then they dumped her body in a water well outside Tal Afar," he said.

According to Edwar, who confirmed Yunus' execution, at least four other women were executed by IS militants in the Mosul area in recent weeks.

Among them were a former candidate for the local council and an academic.

"Women are easy targets for them. Many of the rights activists from Mosul ran away but some of the women among them had to stay with their children," Edwar said.

IS militants have controlled Mosul since June 10, the second day of a major offensive that saw jihadist fighters seize swathes of land in five Iraqi provinces.

They have used the city, Iraq's second largest, as a de facto capital for the Iraqi half of the "caliphate" which their leadership proclaimed in June and also includes large parts of Syria.

"After going after the ethnic and religious minorities, they are now hunting down Sunni members of civil society groups and anyone remotely connected with the government," Edwar said.

She said IS was probably trying to sow maximum fear among the population by openly targeting women.

"When you abduct and kill women, you are really spreading horror," she said.

On September 22, IS executed a women's rights activist, Samira Saleh al-Nuaimi, reportedly because she had condemned the demolition of heritage sites by IS on social media.

Edwar also said two men, a judge and a deputy prosecutor, had been executed over the past two weeks.

A source at the Mosul morgue confirmed that their bodies had been brought in earlier this month.