Hong Kong (CNN) China, Russia and Iran began a four-day joint military exercise in the Indian Ocean and Gulf of Oman on Friday amid ongoing friction in the economically important region between Tehran and Washington.

The Gulf of Oman has been a focal point of geopolitical tensions in 2019, after two oil tankers were attacked in the narrow strait in June by an unidentified party. The US 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.

The vessels planned to leave Iran's Chabahar port in the Gulf of Oman, before being deployed across areas in the north of the Indian Ocean, Second Rear Admiral Gholamreza Tahani said earlier, according to Iran's state-run Press TV.

Tahani said the exercise will cover 17,000 square kilometers and consist of "various tactical exercises," which include target practice and rescuing ships from assaults and fires.

"َAmong the objectives of this exercise are improving the security of international maritime trade, countering maritime piracy and terrorism, exchanging information regarding rescue operations and operational and tactical experience," Tahani added.

Russian President Vladimir Putin, Chinese President Xi Jinping and Iran's President Hassan Rouhani attend a meeting of the Shanghai Cooperation Organisation (SCO) Council of Heads of State in Bishkek on June 14.

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