Three primary adversaries of the U.S. began joint military drills Friday in the Indian Ocean and the Gulf of Oman.

China, Iran and Russia are participating in the exercise, China's defense ministry told several media outlets, including Reuters.

The drill was a “normal military exchange” between the nations and is following international law and practices, Chinese military spokesman Wu Qian said.

The exercises will include target practice and rescuing ships from assaults and fires, according to CNN.

The Gulf of Oman connects to the Strait of Hormuz, through which about one-fifth of the world’s oil passes.

Two oil tankers were attacked in the strait in June. The U.S. blamed Iran for the attack, but Tehran denied the allegations. Then in July, Iran detained a British oil tanker, the Stena Impero, for two months.

Tensions between the U.S. and Iran continue to escalate after President Donald Trump withdrew the U.S. from the controversial 2015 Iranian nuclear deal arranged under his predecessor, Barack Obama.

Trump has reimposed economic sanctions on the Middle Eastern nation.

China, for its part, is facing a crisis in Hong Kong, as six months of anti-Beijing protests continued over the Christmas holidays.

China's human rights violations also have become fodder for Democrats seeking to unseat Trump in 2020. During the most recent Democratic presidential debate, CNN's worldwide live feed was blacked out in the Communist nation when candidates were asked about China's human rights records and recent detentions.