By David Brunnstrom

WASHINGTON (Reuters) - A series of close encounters between the U.S. navy and Iranian combat vessels in the Gulf show the need for Iran and the United States to agree rules of behavior to avoid risky miscalculations, the head of the U.S. Navy said on Monday.

Admiral John Richardson, the U.S. chief of naval operations, said agreements of this type between the United States and Russia and China had helped reduce such risks.

"These are some of these potentially destabilizing things, where a tactical miscalculation, the closer you get to these sorts of things, the margin for error gets smaller and the human error can play a bigger and bigger role," Richardson said


"So it’s very important that we eliminate this kind of activity where we can. There’s nothing good can come from it ... it also advocates the power of a sort of leader-to-leader dialogue."

Years of mutual animosity between Tehran and Washington eased when Washington lifted sanctions on Iran in January after a deal to curb its nuclear ambitions.

But serious differences still remain over Iran's ballistic missile program, and over conflicts in Syria and Iraq and these are reflected in the tense encounters at sea.

Richardson told a seminar at Washington's Center for American Progress think tank it was important for commanders from both sides to have a means through which they can discuss incidents.

"We have the practices to prevent incidents at sea with the Russians ... (and) this Code for Unplanned Encounters with the Chinese ... has been very, very useful," he said.

"Getting some kind of a rule set like that ... with the Iranians, would also be helpful, so that we can have these frameworks for behavior that would guide us more to the useful types of encounters at sea, rather than these 'close aboard' types of demonstrations that really don’t have any positive benefit."

U.S. officials say there have been more than 30 close encounters with Iranian vessels in the Gulf so far this year - more than double the amount from the same period last year.

On Sept. 4, a U.S. Navy coastal patrol ship changed course after a fast-attack craft from Iran's Islamic Revolutionary Guard Corps came within 100 yards (91 meters) in the central Gulf, at least the fourth such incident in less than a month.

The head of U.S. Central Command, General Joseph Votel, said last month that unsafe maneuvers in the Gulf were part of Iranian efforts to exert its influence in the region.

(Reporting by David Brunnstrom)