WASHINGTON • US President Ba-rack Obama has said the fight against the Islamic State in Iraq and Syria (ISIS) will not be over quickly, but states that the group's strategic weaknesses mean it will eventually succumb to a sustained campaign of economic and military pressure.

Speaking after a briefing on Monday from Defence Secretary Ashton Carter, Joint Chiefs of Staff chairman Martin Dempsey and other military commanders, Mr Obama said local troops in Iraq and Syria are key to defeating the extremist group.

"This is a long-term campaign," he said at the Pentagon. ISIS "is opportunistic and it is nimble" .

No amount of military force can dislodge ISIS unless the "underlying conditions" of economic hardship and sectarian strife are addressed in the region, he said, characterising the fight as a "generational struggle".

Recent losses of territory previously held by ISIS prove that the group "can and will be defeated", Mr Obama added.

The President said recent attacks in Tunisia, Kuwait and France emphasised the complex nature of so-called lone-wolf attacks, and the effectiveness of ISIS in targeting disillusioned Muslims across the globe.

His visit to the Pentagon followed a weekend of heavy coalition airstrikes against buildings and transit routes in ISIS' stronghold in eastern Syria.

Mr Carter said on Monday that the strikes helped support Kurdish forces which, in recent days, had made progress on the ground against ISIS.

Mr Obama said the administration was looking for ways to cut off the finances of the terror group.

However, the administration has come under criticism on Capitol Hill as the US and its partners have struggled to recruit local Iraqi and Syrian fighters to combat ISIS.

BLOOMBERG