Beijing accused the Pentagon on Tuesday of "unreasonable" criticism after the return of an underwater drone.
Persistent close-up surveillance and military surveys by the United States within Chinese waters have threatened China's sovereignty and security, causing this and other similar incidents, said Foreign Ministry spokeswoman Hua Chunying.
China has always resolutely opposed and demanded that the US halt these activities, Hua said. "China hopes that the US can respect its security interests."
The drone — retrieved on Thursday by a Chinese vessel 93 kilometers northwest of Subic Bay off the Philippines — was "transferred smoothly" to the US on Tuesday after "friendly negotiation", according to the Defense Ministry.
The Pentagon confirmed the return of the drone in a statement, but it said China had "unlawfully seized" the drone and asked for China to refrain from further efforts to impede lawful US activities.
"As to what the US Defense Department said, I have to verify it with the military. But I think what they said is unreasonable," Hua said.
When asked about the handover, Hua said the resolution of the drone issue showed that "the communication channels between the Chinese and US militaries are relatively smooth and they are beneficial to handling emergencies as well as preventing miscalculations and misunderstandings".
Sino-US relations should head toward "no conflict or confrontation", she added.
Peng Guangqian, a military strategist and a major general of the People's Liberation Army, said the US has taken advantage for years of a gray area in international law to illegally collect oceanic information within Chinese waters.
This information, such as water salinity and current flow, might seem innocent but could influence naval activities, Peng said.
China should develop a strategy to deal with US reconnaissance missions in the South China Sea, which are expected to increase after president-elect Donald Trump takes office on Jan 20, he added.
Tao Wenzhao, a researcher of US studies at the Chinese Academy of Social Sciences, said China conveyed to the US its firm determination to protect national sovereignty and security by resolving the drone episode.
Tao believed China and the US might face more friction in the future and said, "We have to be mentally prepared for anything."