MOSCOW (AP) — Russian and Chinese warships on Thursday practiced joint action in the East China Sea, continuing a series of drills that reflect a growing defense cooperation between the two countries.

The Russian Defense Ministry said the Varyag missile cruiser, the Marshal Shaposhnikov destroyer and two corvettes of Russia’s Pacific Fleet were taking part in the drills that began on Wednesday. China has deployed two destroyers, a diesel submarine and several others ships for the exercise.

Russian and Chinese aircraft were also taking part in the weeklong maneuvers that will involve firing exercises and anti-submarine drills, according to the ministry.

“The main goal of the drills is to strengthen naval cooperation between the Russian Federation and the People’s Republic of China and to maintain peace and stability in the Asia Pacific region,” the ministry said.

Military ties 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. over Taiwan.

In November, Tu-95 bombers of the Russian air force and Chinese H-6K bombers flew joint patrols over the Sea of Japan and the East China Sea. As part of the drills, the Russian bombers landed in China for the first time, and the Chinese bombers flew to an air base in Russia.

In September, China 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.