BEIJING (AP) — China’s Defense Ministry on Monday announced joint naval and air drills with Russia starting this month, underscoring the closeness between their militaries as Russia presses its grinding invasion of Ukraine.

The ministry said the “Northern United-2024” exercises would take place in the Sea of Japan and the Sea of Okhotsk farther north, but gave no details.

It said the naval and air drills aimed to improve strategic cooperation between the two countries and “strengthen their ability to jointly deal with security threats.”

The notice also said the two navies would cruise together in the Pacific, the fifth time they have done so, and together take part in Russia’s “Great Ocean-24” exercise. No details were given.

China has refused to criticize Russia’s full-scale invasion of Ukraine, now in its third year, and blamed the U.S. and NATO for provoking President Vladimir Putin.

While China has not directly provided Russia with arms, it has become a crucial economic lifeline as a top customer for Russian oil and gas as well as a supplier of electronics and other items with both civilian and military uses.

Russia and China, along with other U.S. critics such as Iran, have aligned their foreign policies to challenge and potentially overturn the Western-led liberal democratic order. With joint exercises, Russia has sought Chinese help in achieving its long-cherished aim of becoming a Pacific power, while Moscow has backed China’s territorial claims in the South China Sea and elsewhere.

That has increasingly included the 180-kilometer (110-mile) wide Taiwan Strait that divides mainland China from the self-governing island democracy that Beijing considers its own territory and threatens to invade.

Based on that claim, the Taiwan Strait is Chinese. Though it is not opposed to navigation by others through one of the world’s most heavily trafficked sea ways, China is “firmly opposed to provocations by countries that jeopardize China’s sovereignty and security under the banner of freedom of navigation,” Chinese Foreign Ministry spokesperson Mao Ning said at a daily briefing on Friday.

Mao was responding to a report that a pair of German navy ships were to pass through the strait this month for the first time in more than two decades. The U.S. and virtually every other country, along with Taiwan, considers the strait international waters.