President Donald Trump on Wednesday said the Kurds were "not angels" as he defended his decision to withdraw US troops from northeastern Syria.

Trump's Syria retreat opened the door for a Turkish invasion of Syria that began last Wednesday and targets the Kurds.

"The Kurds are much safer right now. But the Kurds know how to fight, and as I said, they're not angels," Trump said.

"They've got a lot of sand over there," Trump continued. "So there's a lot of sand that they can play with."

The Kurdish-led Syrian Democratic Forces bore the brunt of the US-led campaign against the terrorist group ISIS, losing roughly 11,000 fighters.

President Donald Trump on Wednesday defended his decision to abandon the Kurds, who bore the brunt of the US-led campaign against the terrorist group ISIS and lost roughly 11,000 fighters, by saying they're "not angels."

During a meeting with Italian President Sergio Mattarella, Trump downplayed Turkey's invasion of Syria that began last Wednesday, saying that "it's not our border" and that it "has nothing to do with us."

"The Kurds are much safer right now. But the Kurds know how to fight, and as I said, they're not angels," he added.

"They've got a lot of sand over there," Trump continued. "So there's a lot of sand that they can play with."

Read more: Veterans who fought ISIS say Trump's 'betrayal' of a crucial ally was 'a total slap in the face'

Trump also said his Syria retreat, which has catalyzed a humanitarian crisis and sparked bipartisan criticism in Washington, was "strategically brilliant."

"I view the situation on the Turkish border with Syria to be, for the United States, strategically brilliant," Trump said, less than a week after US forces in Syria came under fire by Turkish artillery.

Turkey invaded Syria three days after the Trump administration abruptly announced a withdrawal of US troops from northeastern Syria. The Syria retreat has been widely characterized as giving Turkey a green light to invade and go after the Kurds.

Read more: Trump defends abandoning the Kurds by saying they didn't help the US in WWII

Trump was warned that the move could create a security vacuum that would open the door for the resurgence of ISIS while benefiting Russia and Syrian President Bashar Assad.

In the week since Turkey invaded, the Kurds have turned to Damascus and Moscow for protection, and ISIS has claimed responsibility for at least two attacks.

Meanwhile, there were reports over the weekend that hundreds of ISIS-linked detainees had escaped a camp in northern Syria. The Kurds have been detaining roughly 11,000 ISIS militants, but they're now focused on thwarting the Turkish assault.

In short, Trump's Syria retreat has been a big geopolitical victory for Russian President Vladimir Putin while offering ISIS an opening for a comeback.