The Denmark-led operation took place Saturday and was coordinated by the Organization for the Prohibition of Chemical Weapons (OPCW). It was conducted in accordance with a UN resolution at the request of the Libyan Government of National Accord (GNA), according to a statement issued by National Security Council spokesman Ned Price.
Price called the 500 tons that was removed "the remains of the chemical weapons stockpile accumulated by Moammar Gadhafi's regime."
A UK naval vessel helped escort the Danish ship bearing the chemicals out of Libya, according to a statement issued by the British government.
The Royal Navy ship "will help ensure chemical weapons precursors do not fall into the hands of extremist groups, including Daesh," UK Defense Secretary Michael Fallon said, using another term for ISIS.
A recent UN-OPCW report accused ISIS of carrying out a chemical weapons attack in Syria.
The OPCW said in a statement that the US, along with nine other countries, assisted through the provision of personnel, technical expertise, equipment, financial and other resources.
A US defense official told CNN that while it was aware of and supportive of the effort, the US military was not involved in the removal operation.
Meanwhile, the Pentagon said Thursday that forces aligned to the GNA continue to make gains against ISIS in its former stronghold in the coastal city of Sirte, Libya.
US Navy Capt. Jeff Davis told reporters that ISIS only retained control over three neighborhoods and that the terror group was being driven into the sea.
"Literally, their backs are against the ocean," Davis said, adding that Libyan naval vessels were preventing ISIS from fleeing via the water.
Davis estimated that less than 200 ISIS fighters remained in the city.
The US has conducted 108 airstrikes against ISIS in Libya since operation Odyssey Lightning began August 1 in at the request of the GNA with four of the strikes taking place Wednesday, Davis said.