The US Navy Friday called off the search for the missing sailor, who is believed to have vanished from the destroyer around 9 a.m. on August 1, in the waters about 140 miles west of Subic Bay in the Philippines.
"I appreciate greatly the dedication and professionalism shown by all who participated in the search efforts", Williams said.
U.S. Navy, Japan Maritime Self-Defense Force and Peoples Liberation Army (Navy) ships and aircraft suspended search efforts at 3 p.m. local August 4.
The Navy is now investigating the incident. The search lasted almost 80 hours and covered roughly 10,000 square nautical miles.
According to Chinese Foreign Ministry spokesperson Lu Kang, the USS Stethem missile destroyer trespassed Chinese territorial waters off the Xisha/Paracel Islands in South China Sea.
The search was called off Friday at 4 p.m. Japan Standard Time, or around 3 a.m.
The Chinese navy and two Japanese military ships aided in the search. Eastern time, officials from 7th Fleet announced.
China claims almost all of the South China Sea, through which about $5 trillion in ship-borne trade passes each year, a stance contested by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.
China said its cooperation in the search for the United States marine was in line with the "Code for Unplanned Encounters at Sea", an agreement between 25 countries - including China and the USA - to reduce and prevent escalation between the countries' navies.
But they were "unable to locate" the sailor after an extensive search, Captain Jeffrey Bennett, commander of Destroyer Squadron 15, said in the statement.
The sailor from the Japan-based United States destroyer Stethem, whose name has not been disclosed, was reported missing in the South China Sea at 9am local time on Tuesday.