China has returned a US underwater drone taken by a Chinese naval vessel in the disputed South China Sea last week after what China's defence ministry said were "friendly" talks between the two countries.
The US acknowledged receipt of the unmanned underwater vehicle and criticised China for the seizure, saying it was "inconsistent with both international law and standards of professionalism for conduct between navies at sea".
China's capture of the drone triggered a diplomatic protest and speculation about whether it will strengthen US President-elect Donald Trump's hand as he seeks a tougher line with Beijing.
A Chinese naval ship took the drone, which the Pentagon says uses unclassified, commercially available technology to collect oceanographic data, on Thursday about 50 nautical miles northwest of Subic Bay in the Philippines.
In a brief statement, China's defence ministry said the drone had been given back to the US.
"After friendly consultations between the Chinese and US sides, the handover work for the US underwater drone was smoothly completed in relevant waters in the South China Sea at midday on December 20," the ministry said.
The Pentagon said the vehicle had been handed over to the guided missile destroyer USS Mustin near where it had been "unlawfully seized".
It called on China to comply with international law and refrain from further efforts to impede lawful US activities.
"The US remains committed to upholding the accepted principles and norms of international law and freedom of navigation and overflight and will continue to fly, sail, and operate in the South China Sea wherever international law allows," Pentagon press secretary Peter Cook said in a statement.
The seizure has added to US concerns about China's growing military presence and aggressive posture in the disputed South China Sea, including its militarisation of maritime outposts.
China is deeply suspicious of any US military activities in the resource-rich South China Sea, with state media and experts saying the use of the drone was likely part of US surveillance efforts in the disputed waterway.
The US Navy has about 130 such underwater drones, made by Teledyne Webb, each weighing about 60kg and able to stay underwater for up to five months.
They are used to collect unclassified data about oceans, including temperature and depth. They are used around the world, but it is unclear how many are used in the South China Sea.
