Photo/Illutration In this photo taken from a video distributed by Russian Defense Ministry Press Service on Dec. 22, a Chinese H-6K strategic bomber flies during a joint patrol mission over the western Pacific. (Russian Defense Ministry Press Service via AP)

MOSCOW--Russian and Chinese bombers flew a joint patrol mission over the western Pacific Tuesday in a show of increasingly close military ties between Moscow and Beijing.

The Russian military said that a pair of its Tu-95 strategic bombers and four Chinese H-6K bombers flew over the Sea of Japan and the East China Sea.

The Russian Defense Ministry said in a statement that the joint mission was intended to “develop and deepen the comprehensive Russia-China partnership, further increase the level of cooperation between the two militaries, expand their ability for joint action and strengthen strategic stability.”

The ministry added that the patrol flight “wasn't directed against any third countries.”

Tuesday's mission was the second such flight since a July 2019 patrol over the same area.

It follows Russian President Vladimir Putin's statement in October that the idea of a future Russia-China military alliance can’t be ruled out--a signal of deepening military cooperation between Moscow and Beijing amid growing tensions in their relations with the United States.

Until that moment, Russia and China had hailed their “strategic partnership,” but rejected any talk about the possibility of their forming a military alliance.

Putin also noted in October that Russia has been sharing highly sensitive military technologies with China that helped significantly bolster its defense capability.

Russia has sought to develop stronger ties with China as its relations with the West sank to post-Cold War lows over Moscow’s annexation of Ukraine’s Crimea, accusations of Russian meddling in the 2016 U.S. presidential election and other issues.

South Korea said it scrambled fighter jets in response to an intrusion into its air defense identification zone by 19 Russian and Chinese military aircraft on Tuesday.

Four Chinese warplanes entered the Korea Air Defense Identification Zone (KADIZ) followed by 15 Russian aircraft, according to South Korea's Joint Chiefs of Staff (JCS).

The South Korean military dispatched air force fighters to take tactical measures.

The South Korean military said the Chinese military had informed South Korea that its planes were carrying out routine training before the Chinese aircraft entered the KADIZ.

"This incident seems to be a joint military drill between China and Russia but it requires a further analysis," the JCS said in a statement.

South Korea's foreign ministry contacted China and Russia and told them there should not be a recurrence, Yonhap news agency reported.

In July last year, South Korean warplanes fired hundreds of warning shots toward Russian military aircraft on a joint air patrol with China, when they entered South Korean airspace.

South Korea and Japan, which both scrambled jets to intercept the patrol at the time, accused Russia and China of violating their airspace. Russia and China denied it.