(Adds more details)

WASHINGTON, April 25 (Reuters) - A cargo ship contracted by the U.S Military Sealift Command fired "a few bursts" of warning shots in the Gulf at small boats believed to be Iranian, U.S. defense officials said on Friday.

"They were able to avoid a serious incident by following the procedures that we use," said Commander Lydia Robertson, a spokeswoman for the U.S. Navy's Bahrain-based Fifth Fleet.

The Westward Venture, a cargo ship chartered by the U.S. Department of Defense, was traveling north in international waters in the central Gulf at around 8 a.m. local time on Thursday when the incident took place, Robertson said.

The ship was approached by two unidentified small boats and its crew issued "standard queries" to the vessels by radio but did not receive a response, she said. The ship then fired a flare, which also produced no response, she said.

The boats continued to approach the cargo ship and its onboard security team fired "a few bursts" of machine gun and rifle warning shots, Robertson said.

"The small boats left the area a short time later," Robertson by telephone.

A U.S. defense official, speaking on condition of anonymity, said the boats were believed to be Iranian.

Shortly after the incident, the ship received a radio query from a ship identifying itself as an Iranian coast guard vessel, Robertson said.

"It is not clear if this was one of the small boats or a separate boat," she said. She said the query from the vessel was conducted correctly.

The United States said in January Iranian boats threatened its warships on Jan. 6 along a vital route for crude oil shipments. (Reporting by Kristin Roberts and Andrew Gray, editing by Lori Santos)

AlertNet news is provided by