Sunni militants continue to march toward Baghdad and take territory from the control of Iraq's central government, committing atrocities as they go.

Rumors of mass killings at the hands of Sunni militants and the Islamic State of Iraq and Syria (ISIS) surfaced June 14 when pictures appeared on social media of ISIS fighters executing captured Iraqi civilians and soldiers. On social media, they claimed to have "exterminated" hundreds, but that could not be confirmed at the time.

Human rights activists now believe the killings took place between June 11 and 14 when the rebels took over the city of Tikrit. According to The Associated Press, Human Rights Watch has confirmed in a statement that the Sunni rebels massacred 150 to 190 people.

"The photos and satellite images from Tikrit provide strong evidence of a horrible war crime that needs further investigation," Human Rights Watch emergencies director Peter Bouckaert said in a statement.

"The number of victims may well be much higher, but the difficulty of locating bodies and accessing the area has prevented a full investigation," HRW said. Though findings are not official, since no investigators are on-site, the Iraqi military confirmed the killings June 15. But the Iraqi military has not spoken of the killings committed by Shiite militants and, possibly, Iraqi security personnel.

Meanwhile, extrajudicial executions, as Amnesty International calls the killings, continue in Iraq. In Mosul, Amnesty senior crisis response adviser Donatella Rovera reported at least 50 killings in and around the city by Shiite militants, as well as retreating Iraqi forces. She interviewed survivors of the attacks in Mosul, Tal'Afar and Ba'quba.

"Reports of multiple incidents where Sunni detainees have been killed in cold blood while in the custody of Iraqi forces are deeply alarming. The killings suggest a worrying pattern of reprisal attacks against Sunnis in retaliation for ISIS gains," she wrote, warning the killers that justice will catch up with them.

Rovera also reported on how ISIS has been fighting as it gains more territory, recounting ISIS shelling neighborhoods where Iraq's religious minorities live. Sunni forces have attacked many residential areas, and hundreds of Christians have fled their homes as ISIS takes town after town.