Iran is investigating a fire that sank one of its largest navy ships early Wednesday in the Gulf of Oman, according to Iranian state media, the latest blow to the country’s vital infrastructure and military assets. Hours after the ship fire, a large fire broke out at an oil refinery near the Iranian capital. Leakage in a liquefied petroleum gas pipeline at the facility caused an explosion and fire, the head of Tehran’s crisis management team told state television. He said that no one had been harmed. It wasn’t immediately clear what caused the fire. Hot summer weather has caused similar fires in the past.

The ship, named the Kharg after an Iranian island, had been deployed to international waters to participate in a training exercise when it caught fire near the port of Jask, the semiofficial Tasnim news agency said. The fire started in the engine room and caused parts of the ship to melt and fall into the sea, state news agency IRNA said. Rescue workers tried for 20 hours to extinguish the fire but couldn’t prevent it from spreading, Tasnim said, citing Iran’s navy. Nearly 400 crew members were evacuated safely from the ship, 33 of them with minor injuries, according to the Hormuzgan governor’s office, which oversees the area where the ship sank.

The commander of the Navy and several senior officers were in the region to investigate the incident, according to IRNA. Other Iranian media outlets broadcast footage from the Gulf of Oman of what they said was the ship burning in the distance. The spokesman for Iran’s mission to the United Nations, Shahrokh Nazemi, declined to comment, and referred to comments made to Iranian media by the Hormuzgan governor’s office.

The Kharg was an oil replenishment tanker, built to enable smaller vessels to embark on extended deployments by supplying them with fuel and dry stores at sea, and capable of carrying large helicopters. Its logistics capacity also made it able to carry heavy cargo, such as military equipment, which could make it suspicious in the eyes of its enemies, U.S. Navy Commander Joshua Himes wrote for the Center for Strategic and International Studies in 2011.

The ship’s sinking follows a string of recent explosions and fires at nuclear and military sites, and attacks on Iranian naval vessels.