Washington (CNN) The fight to liberate the Iraqi of city of Mosul from the grasp of ISIS will be tough but successful, and that will ultimately lead to the terror group's defeat, President Barack Obama said Tuesday in his first remarks on the operation.

"Mosul will be a difficult fight and there will be advances and setbacks," Obama said at a White House Rose Garden news conference with Italian Prime Minister Matteo Renzi, who is being honored with the President's final state dinner. "I am confident, just as ISIL been defeated in communities across Iraq, ISIL will be defeated in Mosul as well, and that will be another step toward their ultimate destruction."

Obama pushed back on criticism that there was adequate planning for the aftermath of the Mosul campaign, even as he acknowledged that Mosul's future will be fraught and a failure to secure it could create the conditions for ISIS' return.

He also tried to reassure the public that ISIS wouldn't wreak more havoc internationally as it feels pinched in its home bases.

Obama thanked the Italian Prime Minister for his country's collaboration in the fight against ISIS, also known as ISIS, as well as on a range of international issues, including maintaining sanctions on Russia for its 2014 moves on Ukraine and eventual annexation of Crimea, a move Italy was less eager to support than some other European countries.

"We discussed the importance of maintaining sanctions on Russia for its invasion of Crimea," Obama said. He said that Italy and the US "are determined to work diplomatically" to resolve that situation.

In an indirect message to Russia, Obama said that he and Renzi, as NATO allies, "discussed our unified determination to defend every ally." He added that Italy will be a key ally working on NATO's Joint Task Force, "which is now operational and can deploy anywhere in Europe on short notice."

The fight for Mosul, which began Sunday, is being led by a diverse 94,000-member coalition comprised of Iraqi security forces, Kurdish Peshmerga allies and thousands of irregulars from various Iraqi minority groups after more than two years of ISIS rule.

Reclaiming Iraq's second-largest city and top stronghold for ISIS could take two months, a Peshmerga military commander told CNN.

"My expectation is two months for the fight inside Mosul, but weather is one of the factors that can delay the process," Sirwan Barzani, a Peshmerga brigadier general, said Tuesday.

Obama stressed the battle's strategic and symbolic importance Tuesday, calling it a "key milestone" in the battle against ISIS.

"The intention is to drive ISIL out of what was its first major urban stronghold and what continues to be one of the key organizational and logistical and leadership hubs for ISIL," he said, using another acronym for the group.

Iraqi forces are "performing effectively and bravely and taking on significant casualties," Obama said.

He tied ISIS' destruction in the Middle East to security in Europe and the United States, saying that the anti-ISIS coalition is "going to drive them back and we are going to drive them out of population centers," so they are no longer able to carry out attacks in other countries.

Obama said there has been extensive planning for the day after Iraqi forces win control of Mosul, saying that there is a "strategic as well as humanitarian interest in us getting this right."

Critics have pilloried the lack of planning for the aftermath of both the 2011 military intervention in Libya, which the Obama administration and its allies undertook, as well as the 2003 invasion of Iraq under then-President George W. Bush.

Renzi said that Mosul's "reconstruction and rebuilding will be a priority with every member of the international community."

The US and its allies have plans in place "that are as extensive as the military plans," Obama said.

"If we're not successful" at this, Obama continued, "that makes us vulnerable to seeing ISIS return and feeding on the resentment."

But Obama said that, despite the preparations, there may still be enormous difficulties in the aftermath of Mosul's defeat.

"Executing will be difficult and no doubt there will be instances where we see some heartbreaking circumstances," he added, describing the human toll of people forced to flee for their lives. "It's hard when you leave your home," he said.