Two U.S. Navy ships collided in the Indian Ocean on Thursday during a routine replenishment operation, a Navy spokesman told the Associated Press.

The supply ships USNS Amelia Earhart and the USNS Walter S. Diehl were participating in an exchange of provisions in the ocean's Gulf of Aden when the collision occurred, Commander Kevin Stephens, spokesman for the U.S. Navy's 5th Fleet, told the AP.

No one was injured and the vessels went on operating with "relatively minor damage," Stephens said.

The cause of the collision was not immediately clear and the incident is being investigated, the Navy said.  

Both ships supply goods for warships belonging to the U.S. 5th Fleet, which is based in Bahrain and covers the Gulf, the Red Sea and the Arabian Sea, according to Reuters. The fleet also belongs to an international naval effort to protect cargo from pirates.

During "underway replenishment" operations, ships usually get within 100 to 150 feet of each other while goods are delivered across cables, the AP reported.