Pictures purport to show massacre of Shia prisoners, as 24 Sunni critics of group are reported killed near Kirkuk.
Fighters from the Islamic State of Iraq and the Levant (ISIL) group have taken partial control of a water dam and the military barracks guarding it in western Anbar province, security sources and witnesses said.
The armed group launched an offensive on the dam late on Friday with explosive-laden vehicles, and engaged in gun battles with Iraqi soldiers that continued through to Saturday.
Dozens of Iraqi troops were killed in the fighting, with poor communications making it difficult to confirm the precise number, Athal al-Fahdawi, an official in Anbar told the Reuters news agency. Army sources said two senior officers were among the dead.
A video posted on YouTube purported to show fighters from the group walking around the dam and the base nearby with no Iraqi soldiers in sight. The bodies of several Iraqi soldiers were seen lying on a road leading to the encampment.
The latest gains by ISIL come amid a new Iraqi government offensive to recapture parts of Anbar from the group. The armed group seized large parts of the mainly Sunni Arab province, during its summer offensive in 2014.
The Iraqi government has had successes, clearing Tikrit in neighbouring Salahuddin province of ISIL fighters, but the group has hit back by attacking Ramadi, the provincial capital of Anbar.
ISIL has also claimed responsibility for multiple suicide car bombings at a border crossing between Iraq and Jordan, killing four soldiers.
The group admitted it was behind the attacks in a video released on Saturday, saying it had targeted a government complex, border crossing control point, and army patrol, according to monitoring group SITE.
A Jordanian official said his government had responded by stepping up security measures at the Tureibil crossing, while an Iraqi defence ministry spokesman said Baghdad would investigate the assault.