Iraqi PM Haidar al-Abadi rejected a call by firebrand Shiite cleric Muqtada al-Sadr to dissolve the Hashd al-Shaabi militia.
"The Hashd al-Shaabi…is for Iraq and will not be dissolved," al-Abadi said in a conference in the capital Baghdad.
"The next phase after liberating the land from Daesh is the battle of the unity of word," he said.
Speaking to supporters on Friday, Sadr called for dissolving Hashd al-Shaabi and absorbing its fighters in the Iraqi army.
Sadr issued the statement after his visit to Saudi Arabia, where he held talks with the kingdom's leadership.
He met Saudi Crown Prince Mohammed bin Salman in the Red Sea port city of Jeddah and discussed issues of common interest, Reuters news agency reported on July 30.
The visit came with the Gulf region embroiled in its worst crisis in years - a dispute between Qatar and four Arab countries led by Saudi Arabia which severed ties with Qatar.
Sadr, an anti-American figure, commands a large following among the urban poor of Baghdad and the southern cities, including Saraya al-Salam, or Peace Brigades militia.
He is now seen as a nationalist who has repeatedly called for protests againstcorruption in the Iraqi government, and his supporters have staged huge protests in Baghdad calling for electoral reform.
On Thursday, Sadr issued a new call for protests in Baghdad and other cities to denounce "corrupt politicians" and demand reforms.
The Hashd al-Shaabi militia was established in 2014 with the avowed purpose of fighting the Daesh terrorist group, which captured vast swathes of territory in northern and western Iraq.
The Shia militia, however, has faced accusations of abuses against civilians in Sunni-majority areas.
Last month, the Iraqi army recaptured Mosul, the country's second largest city, from Daesh, which overran the city in 2014.