Washington-The U.S. and its allies have agreed on a strategy to fight the terrorist ISIS group, according to U.S. Secretary of Defense Ashton Carter.

Carter said on Thursday the objective of the strategy was to destroy ISIS at its base in Mosul, Iraq and in Syria.

However, Carter cautioned that such a step would not completely crush the extreme ideology and the ability of ISIS to launch attacks in other regions.

Carter said the biggest strategic concern voiced at the anti-ISIS coalition was also to plan for the postwar period.

“After ISIS’ defeat,” Carter said, “there will be towns to rebuild, services to reestablish and communities to lead, and the coalition and many others must ensure that the Iraqi and Syrian people have what they need to hold, stabilize and govern their territory.”

Representatives from 30 countries, including Saudi Arabia, had gathered at the State Department in Washington to discuss the latest efforts against ISIS following their first meeting at Joint Base Andrews, Maryland on Wednesday.

After the anti-ISIS coalition meeting, Carter said the attendees agreed on the next phase in their campaign against the terrorist group. “Let me be clear, we have agreed on the necessity of recapturing the cities of Raqqa and Mosul from ISIS,” he said.

Secretary of State John Kerry, who is co-chairing the meeting, said that countries fighting ISIS must do all in their power to wage a historic fight against extremism.

“Today, we can look forward without exaggeration to a time when ISIS is driven completely out of Iraq and Syria,” Kerry said. “We are engaged in an historic effort.”

Kerry said: “Our coalition and partners on the ground have driven ISIS out of nearly 50 percent of the territory that it once controlled in Iraq and 20 percent of the territory in Syria, where it’s obviously more complicated because we don’t have the same forces on the ground.”

The Secretary of State said ISIS would still remain dangerous even when that defeat takes place.

Kerry noted that the setbacks inflicted on ISIS have decreased its fighters by at least a third, slowed recruiting, and increased defections.

The goal of the attendees’ two-day meeting was also to raise more than $2.1 billion in new aid for Iraq.

U.N. Resident Coordinator and Humanitarian Coordinator for Iraq Lise Grande warned that without addressing the needs of Iraqis displaced by the conflict, military victories would be temporary.

“The military campaign will have achieved a great short-term success, but perhaps little else of enduring impact,” she said.

Brett McGurk, the U.S. special presidential envoy to the Global Coalition to Counter ISIS, cautioned that the war against the terrorist group would not be short but long.

The battle for Mosul is expected to be difficult, but the aftermath could be tougher, Iraqi and United Nations and officials say. Plans are being finalized to provide urgent humanitarian aid and restore basic services and security for residents and as many as 2.4 million displaced people.

The U.N. is currently preparing for what it says, could be the biggest humanitarian aid operation this year, as residents already started leaving cities where the Iraqi Army was advancing. Those residents need shelter, food and water for a period ranging from 3 to 12 months.

The U.N. estimates that under a worst-case scenario, more than 1 million people could be displaced from Mosul and another 830,000 from a populated corridor south of the city, adding to the burden of caring for 3.5 million Iraqis already displaced.

ISIS has been controlling Mosul, the second biggest city in Iraq, since June 2014.

On the sidelines of the anti-ISIS coalition meeting, Saudi Deputy Crown Prince Mohammed bin Salman bin Abdulaziz held separate talks on Thursday with Kerry, German Foreign Minister Frank-Walter Steinmeier, and Defense Ministers of the U.S., Ashton Carter, France, Jean-Yves Le Drian, and Britain, Michael Fallon.

Discussions during the meetings focused on the situation in the Middle East.