A retired U.S. general has warned that President Donald Trump's foreign policy in Syria is drifting dangerously close to piracy, following confirmation that American soldiers will be deployed to secure valuable oil fields in the east of the country and protect them from the Islamic State group.

Retired General Barry McCaffrey condemned the plans on Sunday, following Trump's suggestion he wants to bring in Exxon Mobil or another U.S. oil company "to go in there and do it properly...and spread out the wealth" from the oil fields.

Trump's plan has drawn significant criticism, coupled with the withdrawal of U.S. troops from the northeast of the country where their presence had been protecting America's Kurdish-led allies from Turkish attack.

Referencing Trump's comments, McCaffrey asked on Twitter, "WHAT ARE WE BECOMING.... PIRATES?" He also stressed that all oil in the area "belongs to Syria," and noted that even if the remnants of ISIS are defeated, "we lack Congressional authority to stay" in the country.

Secretary of Defense Mark Esper confirmed last week that U.S. troops—supported by armored vehicles—would be deployed to oil fields to stop them falling into the hands of ISIS militants.

Groups of surviving fighters are still waging a guerrilla campaign in both Syria and Iraq, despite Trump's repeated claims that the group has been defeated.

Speaking during a press conference at NATO headquarters in Brussels, Esper said the force would be "mechanized." The Associated Press suggested this could mean several hundred troops will be deployed, likely alongside vehicles such as Bradley armored infantry carriers—and perhaps even tanks.

This would mark a departure from U.S. Syrian deployments in recent years, which have mostly consisted of small groups of special forces equipped with lighter vehicles.

The deployment will also mark another Trump u-turn, putting paid to the president's vow to bring American soldiers home from long-running wars in the Middle East.

The 1,000 troops that had been deployed to Syria have retreated across the border to Iraq, though the government—currently grappling with major civil unrest—has said the Americans do not have permission to stay.

Regardless, Trump has been characteristically bullish in defense of his seemingly erratic Syria policy. "Oil is secured," he tweeted Friday. "Our soldiers have left and are leaving Syria for other places, then.... COMING HOME!"

He continued, "When these pundit fools who have called the Middle East wrong for 20 years ask what we are getting out of the deal, I simply say, THE OIL, AND WE ARE BRINGING OUR SOLDIERS BACK HOME, ISIS SECURED!"

Donald Trump, Syria, oil, piracy, retired general
This file photo shows U.S. troops, accompanied by Kurdish People's Protection Unit fighters, in armoured vehicles near the northern Syrian village of Darbasiyah, on the border with Turkey on April 28, 2017.DELIL SOULEIMAN/AFP/Getty Images/Getty