BEIJING — Four Chinese navy ships have departed for joint drills with Russia in the latest sign of growing cooperation between the two militaries that could challenge the U.S. armed forces’ role in the Asia-Pacific.

A destroyer, missile frigate, supply ship and submarine rescue ship departed Wednesday from the port of Qingdao, home to China’s north sea fleet, the official Xinhua News Agency reported.

The drills are being held in the Sea of Japan near the Korean Peninsula and the Sea of Okhotsk off the northern Japanese island of Hokkaido, Xinhua said.

The exercises are the second stage of an annual joint drill, the first part of which was held July 22-27 in the Baltic Sea — the first time the countries had exercised together in the northern European waterbody.

Russia and China are closely aligned on many diplomatic and security issues, with both countries calling for a negotiated settlement of tensions on the Korean Peninsula, preceded by North Korea suspending its nuclear and missile activities in return for the U.S. and South Korea halting their regular large-scale wargames.

July’s joint drills in the Baltic stirred concern among countries in the region, where tensions are already high over increased displays of military force by both Moscow and NATO.

Both Russia and China say the exercises are not directed at any third parties.

The Chinese ships taking part in the exercises are among the country’s most advanced, components of a growing fleet that poses a significant challenge to the U.S. Navy’s traditional dominance in the Asia-Pacific. Beijing has long chafed at the American presence and is a strong critic of its alliances with Japan, Australia and other countries in the region.

China already has the world’s largest navy, with slightly over 300 vessels, compared to the U.S. Navy’s 277 “deployable battle force ships,” according to the U.S. Naval War College’s China Maritime Studies Institute. The U.S. Office of Naval Intelligence forecasts it will have 313-342 warships by 2020.

While China’s ships are technologically inferior to those of the U.S. Navy, their sheer numbers allow China a significant presence on the open sea, institute professor Andrew S. Erickson wrote in a recent study.

Copyright 2017 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.