ISIS thrives on political chaos, but feeling the pinch: US

Islamic State militant group is trying to capitalise on the "political chaos" prevailing in certain parts of the world to establish footholds in those areas apart from Iraq and Syria, the US has said.

"The US has long been mindful of the strategy that ISIL has used to try to capitalise in other areas where there's political chaos to establish a foothold," White House press secretary Josh Earnest said on Thursday.

"We saw that that's what they were able to successfully do in Syria. And again, that's why we continue to go back to the failed leadership of Bashar al-Assad as the root cause of this chaos and ISIL's growth," he said.

"And we saw they capitalized on some weakness and instability inside of Iraq to spread there. So we've been mindful of the fact that they might be looking to spread other places, like Libya and even like Afghanistan," Earnest said.

"We are going to continue to do that. We're going to continue to watch how the threat in Libya evolves, and we're going to continue to be prepared to take action," he said.

As per the latest White House assessment, the number of fighters fighting on behalf of ISIS in Iraq and in Syria has come down from 31,500 to 25,000 fighters now.

"Now, that means they continue to be a substantial threat, but the potential numbers have declined. And that's a testament to the efforts of our partners on the ground who are taking the fight to ISIL," Earnest said.

"The United States and our coalition partners have taken a number of air strikes that have taken a number of ISIL fighters off the battlefield. ISIL is having more difficult than they've had before in replenishing their ranks," he said.

According to Earnest, ISIL is "trying to establish caliphate inside of Iraq and in Syria. As we apply significant pressure on them there, it will make it harder for them to capitalize on political instability in other places. But right now, we know that they do have that capacity, and that's why we are mindful of the threat that is posed by ISIL in places like Afghanistan and Libya".

President Barack Obama is also ready to use military action and to take military action where necessary to take ISIS fighters off the battlefield, he said.

"Ultimately, a political solution will be required solve the issue. I think that this is a problem that the next President is going to have to deal with from the very beginning," he said.