A shipping company says one of its oil tankers off Saudi Arabia’s port city of Jeddah was hit Monday by an “external source” that caused “an explosion and subsequent fire onboard.”

Hafnia, the owner of the BW Rhine tanker, said in a statement the crew “extinguished the fire with assistance from the shore fire brigade and tugboats.” No one was injured in the blast, but hull damage was reported

The shipping company said it is “possible that some oil has escaped from the vessel,” but added that “instrumentation currently indicates that oil levels on board are at the same level as before the incident.”

It was not immediately clear who or what was responsible for the blast. There have been no claims of responsibility for the explosion. Last month, however, Saudi officials blamed Yemen’s Houthi rebels for a mine blast that damaged a tanker off Saudi Arabia.