The Maritime Self-Defense Force’s Izumo helicopter carrier has joined the United States’ sole forward-deployed aircraft carrier, the USS Ronald Reagan, in joint military exercises in the disputed South China Sea, the MSDF and U.S. 7th Fleet said in separate statements Wednesday.

The drills, which included joint combat training in the waters and airspace of the South China Sea, kicked off on Monday and were due to wrap up Wednesday, the Japanese Defense Ministry said in a statement.

The joint exercises, which were the latest in a spate of multilateral drills in the waters, are likely to be interpreted in Beijing as pushback over China’s moves to extend it’s naval reach further into the Pacific.

They also came just a day after the Defense Ministry said that China’s sole operating aircraft carrier, the Liaoning, had passed through the Miyako Strait between the island of Miyako and Okinawa’s main island as it ventured into the Pacific.

As part of its push further from its shores, China has constructed a series of military outposts in the South China Sea, including islets that include military-grade airfields and advanced weaponry.

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It says these are for defensive purposes, but some experts say this is part of a concerted bid to cement de facto control of the waters.

The waterway includes vital sea lanes through which about $3 trillion in global trade passes each year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims in the waters, where the U.S., Chinese, Japanese and some Southeast Asian navies also routinely operate.

Neither Japan nor the U.S. have claims in the waters, but both allies have routinely stated their commitment to a “free and open Indo-Pacific.”

“The Navy and JMSDF regularly fly, sail and operate together with other allies and partners to promote security and stability throughout the region,” the 7th Fleet said in a statement.

The MSDF’s destroyers Murasame and Akebono joined the Izumo and Reagan in the drills, which also saw several other U.S. vessels take part. The Izumo, together with the Kaga, another helicopter carrier of the same class, are Japan’s largest flat-tops.

This week’s joint drills come on the heels of the MSDF’s two separate quadrilateral naval exercises last month that saw the Izumo link up with vessels from the Australian, French, U.S., Indian and Philippine navies in the South China Sea and in waters west of the Indonesian island of Sumatra.

Japan has worked to bolster its presence in the South China Sea, deploying the Izumo and Murasame as part of the MSDF’s Indo-Pacific deployment this year, which began April 30 and runs through July 10.

“The time we are able to spend at sea training and operating with our partners in the Japan Self Defense Forces is invaluable,” said Capt. Pat Hannifin, the Reagan’s commanding officer. “Our alliance has never been stronger, and it’s never been more important to this region than right now.”