ISIS' leadership dwindling, territory shrinking: US

"ISIL now has no access to international border and this has significantly impacted the overall campaign because they are now a very isolated entity within Syria and it is much harder for them to come in and out, which is critical for them to project their terrorist acts outside of Iraq and Syria," said Brett McGurk, the Special Presidential Envoy for the Global Coalition to Counter ISIS.

"So territory will continue to shrink as we speak and that will continue. ISIL's leadership ranks are dwindling," he told reporters at a White House news conference.

Referring to recent strikes against ISIS leaders in Raqqa, he said since the start of the campaign, the US-led international coalition has eliminated nearly all of ISIS leader Baghdadi's deputies and his trusted advisers.

"That includes his likely successor Haji Iman, his ministers for war, finance, oil and gas security and external operations. While there is still work to be done, ISIS has no longer access to Mediterranean. Raqqa remains ISIL's administrative capital and is under more pressure now than ever before.

"Forces partnered with our coalition have now entirely severed routes between Raqqa and ISIL locations in Iraq, and the Syrian democratic forces, a coalition of local Arabs and Kurds are steadily advancing on Raqqa, with the aim to isolate or really strangulate," McGurk said.

Since the beginning of this campaign about two years ago, the US has trained over 65,000 Iraqi personnel.

"We are now fighting professionally and performing heroically. So, ISIL terrorists are now trapped in Mosul, they are unable to resupply or replenish their dwindling ranks," McGurk said.

In Iraq, about 61 per cent of territory controlled by ISIS has now been reclaimed, he said.

"In Syria, about 28 per cent, but what is most significantly, there was still a 98 kilometre strip of border with Turkey in which ISIL terrorists were still able to come in and out, and that is where the Paris attackers, the Brussels attackers transited through this route.

"So since then, over the last six months we have work very closely with Syrian democratic forces and also with Turkey and a moderate opposition to close off that route. It is at the number one on the map," McGurk said, adding that as ISIS' global cohesion weakens, that of US is strengthening with cooperation across the globe.

"We are having tremendous success against this enemy. It is accelerating. We are now putting pressure on its two so- called capitals of Mosul and Raqqa, simultaneous, relentless pressure that will continue. We are killing their leaders, we are taking off their ability to finance and resource themselves but this remains an unprecedented threat," he said.

"This will remain a multi-year effort," McGurk said, adding that the fight is not over.