Although the Islamic State extremist group is battered and scattered, it cannot be fully defeated until the world finds a way to reconcile and resettle the thousands of people displaced by years of war in Iraq and Syria, the general overseeing American military operations in the Mideast said on Thursday.

Marine Gen. Frank McKenzie, commander of US Central Command, said there is no military means of solving the problem of Mideast refugees and internally displaced persons, or IDPs, who await repatriation or resettlement and represent what he called an unfortunate byproduct of armed conflicts.

“Today, across vast swaths of Syria and Iraq, the systemic indoctrination of IDP and refugee camp populations who are hostage to the receipt of ISIS ideology is an alarming development with potentially generational implications,” McKenzie said in remarks to the National Council on US-Arab Relations.

He said a solution must come from a joint effort by diplomatic, security and humanitarian organizations.

“Unless the international community finds a way to repatriate, reintegrate into home communities, and support locally grown reconciliation programming of these people...we are buying ourselves a strategic problem 10 years down the road when these children grow up radicalised. If we don't address this now, we're never really going to defeat ISIS,” he added.

Over the past six years, starting with former President Barack Obama's decision in 2014 to return US troops to Iraq to halt an advance of Islamic State forces into Iraq from Syria, the US has led an effort to militarily defeat the extremist group in both countries.

But the group has not been extinguished, and McKenzie said it has not abandoned its aspiration to recreate a caliphate and attack the West.

President Donald Trump has pushed for a full US withdrawal from Syria, saying the conflict there was not worth US sacrifices, although there currently are at least several hundred US troops there working with local forces to solidify gains against IS.

The US also has about 3,000 troops still in Iraq; on Tuesday the Pentagon announced that Trump had ordered a drawdown to 2,500 in Iraq with no change for Syria.

President-elect Joe Biden has long argued for bringing most US troops home from the wars in the Middle East and Afghanistan while narrowly focusing the US military on defeating IS and al-Qaida.

Trump has pushed for the repatriation of foreign fighters in Syria, but their home countries have largely refused to take them back. He has shown little interest in leading a diplomatic or humanitarian effort to resettle refugees and internally displaced people and to improve their economic prospects.

In the short run, McKenzie said, IS is in no position to pose a major security threat to the United States. The al-Qaida extremist group and like-minded militants also are severely hobbled but not eliminated, he said.

Pressure put on these groups by the US military and other organisations has made it difficult for them to transfer the funds, organise the plans and move the people needed to conduct external attacks from Iraq or Syria, he said.

“Because when you are running for your life up and down the Euphrates River Valley, listening to the noise of an armed MQ-9 drone overhead, it's hard to think about conducting attack planning against Detroit,” he said.