MOSCOW (AP) — Russian and Chinese strategic bombers on Wednesday flew a joint patrol over the western Pacific in a show of increasingly close defense ties between the two countries.

The Russian Defense Ministry said that the Tu-95 bombers of the Russian air force and the Chinese H-6K bombers flew over the Sea of Japan and the East China Sea during an eight-hour mission.

As part of the drills, the Russian bombers for the first time landed in China and the Chinese bombers flew to an air base in Russia, the ministry said in a statement. It noted that the joint patrols weren't directed against any other country.

China’s Defense Ministry described Wednesday’s patrols as a “routine” part of an annual cooperation plan between the two militaries.

The exercise follows a series of joint drills intended to showcase a growing military cooperation between Moscow and Beijing as they both face tensions with the United States.

In September, Beijing sent more than 2,000 troops along with more than 300 military vehicles, 21 combat aircraft and three warships to take part in a sweeping joint exercise with Russia. The maneuvers marked the first time that China has sent forces from three branches of its military to take part in a single Russian drill, in what was described as a show of the breadth and depth of China-Russia military cooperation and mutual trust.

Defense cooperation between Moscow and Beijing has grown stronger since Russian President Vladimir Putin sent his troops into Ukraine on Feb. 24.

China, which has declared a “no limits” friendship with Russia, has pointedly refused to criticize Moscow’s actions, blaming the U.S. and NATO for provoking the Kremlin, and has blasted the punishing sanctions imposed on Russia.

Russia, in turn, has strongly backed China amid the tensions with the U.S. that followed a visit to Taiwan by U.S. House Speaker Nancy Pelosi.

Washington has warned Beijing against offering Russia direct military or economic assistance, although China’s energy-hungry economy is one of the biggest customers for Russian oil and gas. Its purchases more than doubled compared with a year ago, to $10.2 billion in October, as Chinese importers took advantage of discounts offered by Moscow.

In a letter Tuesday, Chinese President Xi Jinping said Beijing was ready to “forge closer partnership” with Russia in energy, potentially expanding ties.

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