U.S. military conversations continue with China to gain the return of an unmanned underwater drone that was seized by the Chinese Navy last week, the Pentagon said Monday.

Pentagon press secretary Peter Cook said that U.S. and Chinese officials, including military leaders, are working out the logistical details of the exchange. He provided no other specifics.

Cook said the drone was seized illegally by the Chinese, and the U.S. is working to get it returned as quickly as possible.

Final details for where and when the drone can be transferred are being discussed by the U.S. defense attache to China and officials from the Chinese military.

The drone was being operated by civilian contractors collecting unclassified scientific data in international waters in the South China Sea near the Philippines. The USNS Bowditch, which is not a combat ship, was recovering two of the gliders when a Chinese ship approached, launched a small boat and picked up one of the drones, the Pentagon said.

State Department spokesman for East Asia and the Pacific, Justin Higgins, said Monday the seizure of the underwater drone was “unacceptable” and without basis in international law.

“China’s seizure of a U.S. unmanned underwater vehicle (UUV) operating lawfully and in plain sight of a U.S. Navy vessel was unacceptable. China’s action had no basis under international law,” Higgins said.

Higgins said China informed U.S. ambassador to China, Max Baucus, on Saturday morning at approximately 3:30 a.m. EST that China would return the drone.

(AP)