Iraqi Prime Minister Haider al-Abadi, left, speaks during a bilateral meeting at the Lotte New York Palace Hotel in New York, N.Y., on Sept. 19 as President Obama, Vice President Biden, U.S. United Nations Ambassador Samantha Power, and others look on. (Carolyn Kaster/AP)

NEW YORK — President Obama said Monday that the fight to liberate the northern Iraqi city of Mosul could “move forward fairly rapidly,” suggesting that an American-supported, Iraqi-led attack into the city could be imminent.

The Islamic State seized Iraq’s second-largest city in 2014 when Iraqi army troops fled en masse or were slaughtered, shocking U.S. and Iraqi officials who vowed to retake the city. More than two years later, it is still under Islamic State control.

Obama, who is making his  eighth and final visit to the United Nations as president, met with Iraqi Prime Minister Haider al Abadi prior to the gathering of world leaders. “What we have been discussing and focusing on is to go right at the heart of the ISIL operation in Mosul,” Obama said, using the acronym for the Islamic State. “This is going to be a challenging battle, Mosul is a large city.”

Obama said preparations for the fight, including the movement of Iraqi and Kurdish forces into the area, had begun. The most critical phase of the battle likely will come after Islamic State fighters have been forced from the city, when the Iraqis will have to begin the difficult process of rebuilding and governing the region. Mosul is an ethnically and religiously diverse region that has been a center of Sunni rebellion against the Shiite-dominated government in Baghdad.

Obama said he stressed to Abadi the need to rebuild Mosul  in “a way that assures not only ISIL does not come back but that its extremist ideology born out of desperation will not return.” The two leaders also discussed the importance of moving humanitarian aid quickly into the city after the battle.

“It will be a tough fight,” Obama said, according to a White House pool report. “This is going to be hard, this is going to be challenging.”