DUBAI — A major fire that broke out in an oil refinery in the Iranian capital on Wednesday has been brought under control on Thursday, but is still not completely extinguished.

The fires have subsidized considerably, said Hamed Armanfar, the refinery's CEO. Armanfar told state media IRIN on Thursday that the "volume of fires has decreased a lot compared to before, and now only five percent of the initial fires remain," adding that the fire brigades' efforts had successfully prevented the blaze from spreading to other tanks.

The head of Tehran's Provincial Crisis Management Office said that "a leak at a liquid gas pipeline at the facility sparked the fire," Reuters reported. The cause of the blaze will be investigated, Mansour Darajati added, according to Reuters.

No casualties have been reported at the scene, Shaker Khafaei, the head of public relations of Tehran Oil Refining Co., which runs the refinery, told state news agency IRINN. Khafaei also ruled out the possibility of sabotage.

Videos posted on social media Wednesday showed thick smoke circulating in the southern areas of the Iranian capital.

Iran's semi-official Tasnim news agency said all operations had been suspended at the facility, known as the Tondgooyan refinery, Reuters reported.

Some 18 tankers of the refinery caught fire on Wednesday, according to the state-run Young Journalists Club (YJC) agency.

This incident came just hours after one of the largest vessels in the Iranian navy caught fire and sank in the Gulf of Oman on Wednesday.

The "Khark," a huge training and logistical ship, set alight early on Wednesday morning, according to the country's semi-official Fars News Agency. But after 20 hours of an "all-out" rescue effort, the ship sank off the southern Iranian port of Jask, Fars said in its report.

All crew members were evacuated and there were no casualties, it added. — CNN with inputs from agencies