A top Pentagon official on Wednesday said "Islamic State" (ISIS) terrorists in Iraq and Syria are losing the lengthy fight against the US-led coalition, even as the jihadists continue to mount attacks overseas like the one in Brussels last week, AFP reports.

Coalition forces have been hitting ISIS targets since August 2014 after the extremists seized huge parts of Iraq and Syria, and critics have accused the campaign of moving too slowly.

"Right now, without question, the momentum against ISIS is more than at any other time in our campaign," Deputy Defense Secretary Robert Work said, using an acronym for the IS group. "We are more confident than ever that militarily, ISIS is on its way to a defeat on the battlefield."