A nuclear submarine was damaged in a collision with another U.S. Navy vessel off the coast of Iran early Friday, leaving 15 U.S. sailors injured and 25,000 gallons of fuel spilling into the Strait of Hormuz.

The USS Hartford, a nuclear-powered fast-attack submarine, was fully submerged Friday when it collided with the transport ship the USS New Orleans, according to a Navy official in the 5th Fleet. Seas were calm but visibility was low as the incident occurred around 1:00 a.m. local time.

No official reason has been given for the accident but a Defense Department official told FOX News that "it appears the two vessels were not in communication before they collided."

Fifteen sailors aboard the Hartford were slightly injured but able to return to duty. No injuries were reported aboard the New Orleans, according to the Bahrain-based 5th Fleet. It was the Los Angeles-class submarine's first deployment.

There was no damage to the nuclear reactor powering the Hartford, said Lt. Nate Christensen, spokesman for the 5th Fleet, but the collision ruptured one of the many fuel tanks of the USS New Orleans. Officials say there are no real plans yet for cleaning up the 25,000 gallons of diesel fuel that have spilled into the Persian Gulf.

Both ships were heading to port when the incident occurred. Navy officials said it did not appear that the sub was surfacing at the time of the incident. Officials could not say how deep the water was at the point of impact.

Both vessels are currently operating under their own power and heading to port for repairs and evaluation, but Christensen said that following standard security procedures he could not say where the vessels were heading.

The Navy said both ships were on regularly scheduled deployments to the region and conducting security operations.

Oil prices rose after news of the collision which happened in a busy shipping route.

As much as 17 million barrels of oil a day went through the narrow strait in the first half of 2008, or about 40 percent of all seaborne traded oil or 20 percent of all oil traded globally.

The Hartford is based in Groton, Conn. and the New Orleans is based in San Diego, Calif., the Navy said.

FOX News' Justin Fishel and the Associated Press contributed to this report.