At least 150 women who refused to marry fighters belonging to the Islamic State (IS) group have been executed in the western Iraqi province of Anbar, the country's Ministry of Human Rights reported.

According to a ministry statement released on Tuesday, IS fighters carried out a number of attacks in Fallujah and buried the victims in mass graves in one of the city’s neighbourhoods.

"At least 150 females, including pregnant women, were executed in Fallujah by a militant named Abu Anas Al-Libi after they refused to accept jihad marriage," the statement said.

"Many families were also forced to migrate from the province’s northern town of al-Wafa after hundreds of residents received death threats."

The ministry also said many children died when their families were stranded in the desert after leaving their homes.

Also on Tuesday, Iraqi security forces launched an attack against IS fighters in Ramadi, Anbar province's capital city, a security source told Anadolu news agency.

"Iraqi security forces from the army and police, supported by tribal fighters, have killed 13 [IS] militants, while seven other militants surrendered," Anbar police chief Kazim al-Fahdawi said.

A suicide bomber was also killed while attempting to approach a security area, al-Fahdawi added. "The suicide attacker was shot dead immediately, and his explosive belt did not cause any casualties."

Despite US-led air strikes against the group in Iraq and neighbouring Syria, IS has maintained control over many areas in Anbar province, and is attempting to take over Ramadi.

IS seized vast swathes of Iraqi territory after capturing the country's second-largest city, Mosul, in June.

As a result of the fighting, residents of Mosul have begun migrating to Rakka in Syria, which is also under IS control.

"The inhabitants of Mosul feel that their lives are at risk, because of the US-led international coalition’s air strikes which target [IS] in the city. The inhabitants concerns have increased as [IS] fortified its positions, and started to dig a ditch around the city," Mosul's police chief, Brigadier Gen. Mazza al-Nun, said.

Mosul’s police forces are being re-established in a camp approximately 20 kilometres north of the city, while a ground offensive to retake the city is expected in the near future.