DUBAI, United Arab Emirates >> China, Iran and Russia have begun a joint naval drill in the Gulf of Oman, a crucial waterway near the mouth of the Persian Gulf, officials said Tuesday.

Footage aired by Chinese state television and a video released by the Russian navy showed the ongoing drill, known as “Marine Security Belt 2024.”

China sent the guided-missile destroyer Urumqi and the guided-missile frigate Linyi to the exercise. Russia’s forces are being led by the Varyag, a Slava-class cruiser.

More than 20 ships, support vessels and combat boats from the three countries, as well as naval helicopters, are involved in the exercise.

A report by Iranian state television quoted the drill’s spokesperson, Adm. Mostafa Tajaddini, as saying the drill will take place in 17,000 square kilometers (6,600 square miles) of water.

Tajaddini added that the three nations’ drill — their fourth since 2019 — was also meant to improve trade, confront “piracy and terrorism, support to humanitarian activities and the exchange of information in the field of rescue,” among other goals.

Iran has stepped up its military cooperation with Beijing and Moscow in response to regional tensions with the United States, including due to supplying military drones to Russia now being used in Moscow’s war on Ukraine.

Azerbaijan, Kazakhstan, Oman, Pakistan and South Africa are observers of the drill.

The Gulf of Oman has seen a series of attacks since 2019 that the U.S. has blamed on Iran, as well as ship seizures by Tehran, since the collapse of its nuclear deal with world powers. A fifth of all oil traded passes through the Strait of Hormuz, the Persian Gulf’s narrow mouth.