Mustafa al-Kadhimi arrived on his first official visit abroad since taking office more than two months ago, Iranian media reported.
State television showed footage of Mr al-Kadhimi landing at Tehran’s Mehrabad airport. The TV outlet said he would meet top Iranian leaders, including Supreme Leader Ayatollah Ali Khamenei and Mr Rouhani.
The official website of the office of the Iranian presidency later released a photo of Mr Rouhani and Mr al-Kadhimi at a welcome ceremony in Tehran, showing both wearing protective face masks to help prevent the spread of coronavirus.
“We are certain that the visit will be a turning point in relations between the two countries,” Mr Rouhani said after meeting the Iraqi premier. “We still remain ready to stand by the Iraqi nation and apply efforts for stability and security in Iraq and the region.”
Mr Al-Kadhimi replied: “Iraq will not allow the posing of any threat from its soil against Iran.”
The visit came after Iranian foreign minister Mohammad Javad Zarif travelled to Baghdad over the weekend.
It was Mr Zarif’s first visit to Iraq since a US air strike in January killed top Iranian general Qassim Soleimani outside Baghdad’s international airport. The strike catapulted Iraq to the brink of a US-Iran proxy war that could have destabilised the Middle East.
In Baghdad, Mr Zarif paid a visit to the site where Mr Soleimani was killed, saying “Iran-Iraq relations will not be shaken” despite the general’s death.
Mr Soleimani led Iran’s expeditionary Quds Force and was the architect of its regional military activities.
Iran sees Iraq as a possible route to bypass US sanctions that President Donald Trump reimposed on Tehran in 2018 after pulling America out of the 2015 nuclear deal.