A general view shows the USS Bonhomme Richard, during a port call in waters off Hong Kong.

China has returned a U.S. underwater drone taken by a Chinese naval vessel in the South China Sea last week after "friendly" talks between the two countries, China's Defence Ministry said on Tuesday.

China's seizure of the unmanned underwater vehicle (UUV) triggered a diplomatic protest and speculation about whether it will strengthen U.S. 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 statement, Pentagon press secretary Peter Cook said that while the U.S. acknowledged the drone's return, "this incident was inconsistent with both international law and standards of professionalism for conduct between navies at sea."

"The U.S. will continue to investigate the events surrounding this incident and address any additional findings with the Chinese, as part of our ongoing diplomatic dialogues and the Military Maritime Consultative Agreement Mechanism."



In a brief statement, China's Defence Ministry said the drone had been given back to the United States.

