The destruction of an historic mosque in Mosul and the unverified death of a militant leader are pointing to the end of the Islamic State in Iraq.

Islamic State blew up the Grand al-Nuri Mosque and its famous leaning minaret where the Iraqi militant leader – Abu Bakr al-Baghdadi – declared a self-style caliphate in 2014.

The reports come after Russia claimed to have killed al-Baghdadi, the leader of Islamic State in Iraq, in an airstrike in Syria last month.

Militants destroyed the medieval mosque as Iraqi forces trying to expel the group from Mosul closed in on the site.

“Blowing up the al-Hadba minaret and the al-Nuri mosque amounts to an official acknowledgement of defeat,” the Iraqi prime minister said on his website.

Russia’s claim to have killed al-Baghdadi on May 28 is yet to be confirmed.

The airstrike hit the outskirts of Ragga, in Syria, at a command post where ISIS leaders were meeting, a Kremlin ministry statement said, CNN reported.

“According to information that is being verified through various channels, the leader of ISIS … Abu Bakr al-Baghdadi was also present at the meeting and was killed as a result of the strike,” the statement said.

Islamic State jihadist group blew up Mosul’s iconic leaning minaret and the adjacent mosque. Photo: AAP

Islamic State in Iraq leader Abu Bakr al-Baghdadi is pictured in an image released in July, 2014. Photo: Getty

The United States is investigating the claim.

There have previously been false reports of al-Baghdadi’s death.

Baghdadi’s black flag had flown over the Grand al-Nuri Mosque, which was blown up on Wednesday night, since June 2014.

Islamic State’s Amaq news agency accused US aircraft of destroying the mosque on Wednesday night, a claim swiftly denied by the US-led coalition fighting the militant group.

Iraq’s military distributed a picture taken from the air that appeared to show the mosque and minaret reduce to rubble among the small houses of the Old City, where the militants are under siege.

A video seen on social media showed the minaret collapsing in a belch of sand and dust as a woman lamented in the background: “The minaret, the minaret, the minaret.”

The mosque was destroyed as Iraq’s Counter Terrorism Service units, which have been battling their way through Mosul’s Old City, came within 50 metres of it, according to the Iraqi military.

Iraqi forces said on Wednesday they had started to push towards the mosque.

The forces on Tuesday had encircled the jihadist group’s stronghold in the Old City, the last district under Islamic State control in Mosul.

– with AAP

The Grand al-Nuri Mosque and its famous leaning minaret in Mosul, Iraq, is pictured before being blown up by the Islamic State on Wednesday night. Photo: Getty