The Iraqi defence ministry said it had received delegations led by their respective deputy chiefs of staff, to "strengthen cooperation and coordination in terms of security and intelligence between these countries".

Russia is fighting rebels and jihadists in Syria alongside President Bashar al-Assad's forces, while Iran is a key ally of both Baghdad and Damascus.

The four countries had created joint operations rooms to coordinate the fight against IS, now driven out of all urban centres in Iraq and largely confined to desert holdouts in Syria.

In a rare address last month, the jihadist group's leader Abu Bakr al-Baghdadi urged his followers to continue their fight.

According to jihadist expert Hisham al-Hashemi, there are still 2,000 IS fighters -- nearly all of them Iraqi -- active in four regions of Iraq.

Their aim is "to take revenge on those that ousted them", he said.

Despite major setbacks in Iraq and Syria, in July IS managed to carry out a string of coordinated attacks in southern Syria that killed more than 250 people.