He made the remark on Sunday in an address to the 29th International Islamic Unity Conference in Tehran, adding that the Iraqi people are fighting terrorist elements from over 70 countries.
He said terrorists are at war with innocent people, noting that they brutally attack schools, marketplaces and other civilian targets.
Iraq has been facing the growing threat of terrorism, mainly posed by the ISIL Takfiri group.
ISIL, also known as the Daesh or ISIS, made advances in northern and western Iraq in summer 2014 after capturing swaths of northern Syria.
The Takfiri terrorists have been committing heinous crimes under the name of Islam. They consider Shiites and even Sunni Muslims to be infidels.
Apart from direct involvement in military offensive against different Iraqi and Syrian cities, the ISIL Takfiri terrorists seek to fuel sectarian conflicts wherever they conquer.
In the meantime, a combination of concentrated attacks by the Iraqi military and the volunteer forces, who rushed to take arms after top Iraqi cleric Ayatollah Ali al-Sistani issued a fatwa calling for fight against the militants, have blunted the edge of the ISIL offensive.
Elsewhere in his remarks, al-Jaafari underlined the need for enhancing Islamic unity, saying that it is possible through taking recourse to the Holy Quran and Ahl-ul-Bayt (AS).
The 29th International Islamic Unity Conference kicked off in Tehran on Sunday with the participation of hundreds of Shia and Sunni scholars and thinkers.
The current crises facing the Islamic world are the main subjects to be discussed in the international event, which will last until Tuesday.