Pro-government Iraqi forces will recapture the strategic city of Ramadi from
Asked how long it would take to wrest the Anbar provincial capital back from the extremists, Abadi told the BBC: "I'm talking about days now."
The Iraqi leader added: "It makes my heart bleed because we lost Ramadi. But I can assure you we can bring it back soon."
Abadi also rejected comments from U.S. Defense Secretary Ashton Carter to CNN that Iraqi forces "showed no will to fight" in Ramadi.
"I am sure he [Carter] was fed with the wrong information," the Iraqi prime minister said of the U.S. defense chief's scathing comments.
The loss last week of Ramadi was a major embarrassment for the government of Abadi, who took office last year with strong U.S. and international backing. A barrage of U.S.-led airstrikes in and around the city didn't avert Ramadi's fall.
Video images of Iraqi forces in Humvees in full-throttle withdrawal from Ramadi while a much smaller militant force swept through the city rekindled memories of the battlefield debacle last June, when Iraqi troops retreated ignominiously from the northern city of Mosul and elsewhere. Mosul, a city of more than 1 million, remains an Islamic State stronghold.
Iraqi troops and allied militias, mostly Shiite, have been massing for a counter-offensive to retake Ramadi, which is situated about 70 miles west of Baghdad, in Iraq's Sunni heartland.
Sunni discontent with Iraq's Shiite-led central government has aided the Islamic State, an ultra-fundamentalist Al Qaeda breakaway faction. Islamic State purports to represent Sunni interests and regards Shiites, the majority sect in Iraq, as heretics. The sectarian rift has bedeviled Iraq since the 2003 U.S.-led invasion ousted ex-strongman Saddam Hussein, a Sunni who repressed Shiite and other opposition political movements and was a fierce adversary of Shiite Iran, Iraq's neighbor. Many of Hussein's' former military commanders are believed to have forged alliances with Islamic State.
Analysts in Iraq and elsewhere have cautioned that an operation to retake Ramadi -- once a city of almost 500,000, though now largely depopulated -- could drag on for some time against well-entrenched militants adept at urban warfare and slowing down attackers with explosives planted in buildings and vehicles. It took a large pro-government Iraq force several weeks in March to recapture the smaller city of Tikrit, also a largely Sunni town. In Tikrit, as in Ramadi, loyalist fighters also greatly outnumbered Islamic State forces.
In recent days, the Iraqi army and allied militias have already retaken some areas and positions outside Ramadi while mobilizing for a larger offensive.
The Iraqi prime minister insisted that pro-government forces, who have suffered thousands of casualties in the battle against Islamic State, have the determination to fight. But he said that Islamic State's trademark tactic of detonating massive vehicular suicide bombs has had a demoralizing effect.
"They have the will to fight but when they are faced with an onslaught by [Islamic State] from nowhere ... with armored trucks packed with explosives, the effect of them is like a small nuclear bomb," Abadi told the BBC. "It gives a very bad effect on our forces."
Many militants have been slipping into Iraq from neighboring Syria through a frontier that is largely under Islamic State control, the Iraqi leader said. "We've asked our international coalition partners to tighten control over the border," Abadi said.
Islamic State, which arose from the chaos in neighboring Syria, holds sway over vast stretches of territory in Iraq and Syria. Both the Iraqi and Syrian governments, aided by international partners, are fighting to oust Islamic State in a complex geopolitical struggle.
The U.S.-led coalition conducting near-daily aerial bombardment targeting Islamic State positions in Iraq and Syria coordinates its efforts with the Iraqi government in Baghdad but not with its ally, the administration of Syrian President
Iran, another major player in the battle against Islamic State, is providing military aid to both the Iraqi and Syrian governments. The Obama administration says it does not coordinate with Iran.
Tens of thousands of civilians have fled Ramadi and surrounding areas in the Euphrates River valley, exacerbating Iraq's crisis of displaced multitudes in the almost year-long battle against Islamic State.
Islamic State has also made recent gains in Syria, capturing the desert city of Palmyra, site of fabled, Roman-era ruins that are a United Nations World Heritage site. In recent days, Syrian and other media have reported, militants have slain hundreds of civilians and suspected Syrian government collaborators in and around Palmyra.