A week of eventful news from Iraq — including the Islamic State’s threat to take the western Iraqi city of Ramadi and attack on the Baiji oil refinery, as well as Prime Minister Haider al-Abadi’s visit to the White House — has been overtaken on Friday by claims of the death of Izzat al-Douri, a former deputy to Saddam Hussein who became an ally of the Islamic State.

Photographs purportedly of the slain al-Douri are spreading across the Internet, while the Governor of Salaheddin Province has claimed confirmation of the death of a “mastermind of Islamic State in Iraq”.

The Governor said DNA tests would further confirm the identity of al-Douri, whose body is reportedly with the Shia militia Badr Brigades.

Douri, 72, was the Vice-Chairman of Saddam Hussein’s top governing body, the Revolutionary Command Council. He became a fugitive after the US-led invasion in 2003, and is widely believed to have been a leader of the insurgency against both the American occupation and successive governments in Baghdad.

In spring 2004, al-Douri was said to have allied with the Islamic State as they made their lightning offensive across northern and eastern Iraq, as well as challenging Iraqi forces in Anbar Province in the west.

If confirmed, Douri’s death will be a check on the fortunes of the Islamic State after their dramatic gains this week on both the western and northern fronts.

On Wednesday, the jihadist took villages on the eastern edge of Ramadi, the provincial capital of Anbar, as more than 2,000 families fled the city. Officials said Ramadi was now a ghost town, with empty streets and closed shops.

The Islamic State took the nearby city of Fallujah at the start of 2014, foreshadowing its spread across Iraq.

In northern Iraq, the jihadists continued their attack on the Baiji refinery, one of three in Iraq and the main handler of oil from the north. Earlier this week, the fighters blasted their way through the perimeter and took control of several installations, including a distribution point and storage tanks.

A source in the military operations command for Salahuddin Province said an Iraqi army battalion had arrived to help defend the refinery on Thursday. He claimed the Islamic State had not been able to take any major infrastructure.

Islamic State sympathizers circulated photographs on social media appearing to show fighters inside the complex with the caption, “The soldiers of the State advance to cleanse what is left of Baiji refinery.”