If the Anbar provincial capital can be fully secured and re-populated, it would be the first major success for the US-trained force that fled 18 months ago as self-proclaimed Islamic State militants surged through northern and western Iraq.
Security forces must still remove explosives planted in streets and buildings and clear out fighters in some densely built-up areas, and much of the infrastructure needs to be rebuilt.
Three mortar rounds landed about 500 metres from Abadi's location during his visit, three security sources said. The prime minister was not in danger but was forced to leave the area, they said.
Abadi had arrived in Ramadi by helicopter. He moved through the city with the Anbar governor and top security officials in a convoy of Humvees, crossing a floating bridge used by the armed forces last week to retake the city center.
He met soldiers at the main government complex captured by counter-terrorism forces on Monday and planted the tri-color flag outside the building.
He had announced the visit to Ramadi himself on Twitter and declared Thursday a national holiday in celebration.
The army's apparent capture of Ramadi, in the Euphrates River valley west of Baghdad, marks a milestone for the forces, which crumbled when the hardline Sunni Muslim militants seized a third of Iraq in June 2014.
In battles since then, Iraq's armed forces had operated mainly in a supporting role beside powerful Iranian-backed Shi'ite Muslim militias.
Hisham al-Hashimi, a Baghdad-based analyst who has worked with the Iraqi government, said the retaking of Ramadi suggested Abadi's strategy of heavy U.S. air support while sidelining the Shi'ite militias, which have served as a bulwark against Islamic State but drawn objections from Washington, could be effective.
"Ramadi is an example that the regular army wishes to promote for upcoming battles of liberation," said Hashimi.
'Excited about this victory'
Ramadi was the only city to have fallen under Islamic State control since Abadi took office in September 2014.
"He is excited about this victory, because he managed to remove this blot from his historical record as commander-in-chief of the armed forces," said Hashimi.
Abadi's Shi'ite-led government has said for months it would prove the rebuilt capability of the army by reversing militant gains in Anbar, a mainly Sunni, largely desert province stretching to the borders of Syria, Saudi Arabia and Jordan.
As part of his security reforms, Abadi last year scrapped 50,000 "ghost soldiers" - army members who don't actually exist but whose salaries are collected - and changed security chiefs in a bid to improve performance. But he has faced resistance to dismantling a patronage system and rooting out incompetence in the security apparatus and other state organs.
Iraqi forces, though backed by US-led coalition air strikes, had been slowed in Ramadi by bombs planted in streets and booby-trapped buildings by Islamic State fighters. Iraqi and U.S. officials have said pockets of insurgents held up in the city and its outskirts still needed to be cleared.
US Army Colonel Steve Warren, spokesman for the international coalition backing Baghdad, said casualties to Iraqi forces during the battle were in the low double digits. He and Iraqi officials put Islamic State casualties in the hundreds.
Reuters could not independently confirm those estimates.
The government has said local Sunni tribal fighters would comprise the main holding force in Ramadi, a role played in other areas taken from Islamic State by mainly Iranian-backed Shi'ite armed groups which have been held back from Ramadi for fear of stoking sectarian tensions.
Such a strategy would echo the U.S. military's "surge" campaign of 2006-2007, which relied on recruiting and arming Sunni tribal fighters against al Qaeda, Islamic State's precursor. Anbar, including Ramadi, was a major focus of that campaign at the height of the 2003-2011 U.S. war in Iraq.
While the earlier Sunni tribal force numbered in the tens of thousands, only a few thousand fighters have so far been prepared to operate in Ramadi this time.
