China and Russia conducted joint air force patrols over the Sea of Japan and the East China Sea on Tuesday, as South Korea said it had deployed warplanes in response to fighter jets allegedly near its airspace.

In a statement, the Chinese Defense Ministry said Beijing and Moscow "staged the sixth joint aerial patrol in accordance with an annual military cooperation plan between China and Russia."

The statement gave no further details of the drills, which took place over waters bordering Japan, the Korean peninsula, and Taiwan.

South Korea claimed that four Russian and four Chinese military aircraft had entered its air defense identification zone (ADIZ) around lunchtime on Tuesday, prompting it to scramble warplanes.

According to AFP, an ADIZ is an area wider than a country's airspace in which it tries to control aircraft for security reasons, but the concept is not defined in any international treaty.

The South Korean military "identified the Chinese and Russian jets before their entry into the air identification zone," Seoul's Joint Chiefs of Staff (JCS) said.

"We deployed air force fighters to conduct tactical steps in preparation in case of an emergency," it added.

The JCS confirmed that the eight foreign jets did not violate Seoul's airspace.

The incident comes after the defense ministers of South Korea, Japan, and the United States on Saturday agreed to set up real-time data sharing on DPRK missile launches by the end of the year.

Asked about the Russia-China air patrols, State Department Spokesperson Vedant Patel said the United States was committed to working with Japan and South Korea towards "a free and open Indo-Pacific" and that the allies were aware of any actions "that can be interpreted as destabilizing or reckless."

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