Iran and Iraq on Sunday signed deals aimed at boosting military cooperation during a visit by Baghdad's Defence Minister Irfan al-Hayali to Tehran.

In a memorandum of understanding signed by Hayali and his Iranian counterpart Hossein Dehghan, the neighbours agreed on a "wide range of military and defence cooperation" including the "fight against terrorism and extremism," state news agency IRNA reported.

Hayali, who was leading a military delegation, also met separately with parliament speaker Ali Larijani and Ali Shamkhani, secretary of Iran's Supreme National Security Council.

Larijani and Shamkhani emphasised the importance of "unity".

"Iran supports the unity of all groups and ethnicities in Iraq," the state broadcaster's website quoted Larijani as telling Hayali.

Larijani also underlined the importance of preserving Iraqi unity "because if it wasn't for the emergence of political differences, the (Islamic State group) would not have been able to penetrate there".

The Iraqi minister acknowledged Iran's help in the fight against IS and also stressed the importance of unity.

Iraq's Kurdistan region has announced it will hold an independence referendum in September.

"We will not let any political side disintegrate Iraq," Hayali said.

In his talks with Hayali, Shamkhani warned that "secessionist approaches can become a platform... to prepare the ground for insecurity and instability".

Tehran has been a key supporter of Baghdad in its fight against IS and has provided Iraq with financial and military help.

Iran has its own Kurdish population along its borders with Iraq and Turkey, and does not want to see Iraq's Kurdish region become an independent state.