Walid al-Moallem made the demand in an address at the U.N General Assembly Saturday.
There are about 1,000 U.S. troops in Syria to battle Islamic State militants. Turkey has forces in Syria targeting ISIS and Kurdish fighters.
"The United States and Turkey maintain an illegal military presence in northern Syria." al-Moallem told the U.N. General Assembly on Saturday. "Any foreign forces operating in our territories without our authorization are occupying forces and should withdraw immediately."
“If they refuse, we have the right to take any and all countermeasures authorized under international law,” he said.
Over more than eight years, Syria's devastating civil war has drawn numerous foreign militaries and thousands of foreign fighters battling for power.
Most of the country has returned to government control. But rebels and extremists still hold Idlib in the northwest, and the oil-rich northeast, held by U.S.-backed Kurdish groups.
President Trump last year ordered the complete withdrawal of U.S. troops from Syria – but then agreed to let some forces remain to ensure ISIS militants cannot regroup, Reuters reported.
The Associated Press contributed to this report.