'ISIS is not defeated. We have got to keep the pressure on ISIS so they don't recover,' Mattis told Chuck Todd Saturday on Meet The Press when asked if President Trump made the right decision by pulling troops from Northern Syria last week.
'It's in a situation of disarray right now,' Mattis, who resigned as Secretary of Defense in January, said of the situation between Turkey and Syria.
'Obviously the Kurds are adapting to the Turkish attacks. We'll have to see if they can maintain the fight against ISIS. It's going to have an impact. The question is how much.
'We may want a war over; we may even declare it over. You can pull your troops out as President Obama learned the hard way out of Iraq, but the ''enemy gets the vote'', we say in the military. And in this case, if we don't keep the pressure on, then ISIS will resurge. It's absolutely a given that they will come back.'
Former Secretary of Defense James Mattis warned Saturday that ISIS will 'absolutely come back' with the removal of U.S. troops from Syria
'ISIS is not defeated. We have got to keep the pressure on ISIS so they don't recover,' he told Chuck Todd on Meet The Press. Pictured are Syrian protesters carrying a banner that reads 'the north and east of Syria will become a cemetery from Erdogan and Daech'
On Thursday, President Trump defended his decision to withdraw U.S. troops from northern Syria and abandon America's Kurdish allies to a Turkish invasion because 'they didn't help us with Normandy'.
The President insisted that he likes the Kurds - who led the fight against ISIS alongside the US - but added that they had been acting in their own self-interest in battling ISIS and it was time for them to continue the fight alone.
Trump also suggested that he isn't worried about ISIS fighters being held by the Kurds escaping amid Turkish attacks, because 'they'll go back to Europe.'
'That's where they want to go, they want to go back to their homes, but Europe didn't want them' he said on Wednesday night.
'For months we could have given it to them, they could have had trials, they could have done whatever they wanted, but as usual it's not reciprocal.
'That's all I want, I don't want an edge I just want reciprocal... It's not a fair deal for the United States.'
Trump spoke out just hours after Turkey began bombing Kurdish strongholds in northern Syria and marched troops across the border in order to establish a 'peace corridor' in the north of the country.
On Thursday, Donald Trump defended his decision to abandon America's Kurdish allies in Syria to a Turkish invasion because 'they didn't help us in Normandy'
The Kurdish-led Syrian Democratic Forces reported multiple Turkish bombing raids against their strongholds on Wednesday, saying multiple civilians were killed
It comes after Trump agreed to withdraw US troops from the region and hand security operations over to Turkey during a routine call with President Erdogan.
Erdogan says he wants to drive terrorists - by which he means the Kurdish-led Syrian Democratic Forces - away from Turkey's border so he can resettle some 2million Syrian refugees there.
But critics agree with Mattis, saying the move will destabilize the region, lead to civilians being killed, and may cause an ISIS resurgence.
Of particular concern are prison camps being run by the SDF which contain some 10,000 ISIS fighters, around 2,500 of them foreigners - mainly from Europe.
Under Trump's plan, Turkey would take responsibility for these prisoners.
'The Kurds are fighting for their land,' Trump told reporters gathered in the Roosevelt Room of the White House for a briefing about business deregulation.