By Mohammed Abbas

ABOARD USS NIMITZ, June 7 (Reuters) - Despite the growing war of words between Iran and the United States, their navies talk almost daily to try to avoid an accidental conflict.

U.S. ships have kept in close contact with Iranian counterparts during two weeks of war games in the Gulf that amount to Washington's biggest show of naval force in the region since the 2003 Iraq war.

"You are trying to reduce the chance that an event could occur that could be catastrophic for all concerned," said Rear Admiral John Blake, commander of the Nimitz aircraft carrier strike group.

"We talk to the Iranians on an almost daily basis, just as we talk to the Omanis and the other navies," he said. "All my communications with them have been cordial and professional."

The war games, now winding down, have been held just off Iran and near the Strait of Hormuz -- a vital route from the region that provides a third of the world's sea-borne oil.

It is also the place where the U.S. warship Vincennes shot down an Iranian airliner in 1988, killing all 290 on board, in what Washington said was an accident after crew mistook the plane for a fighter. Tehran called it a deliberate attack.

GROWING TENSIONS

The United States severed diplomatic ties with Iran after the 1979 revolution that ushered in the Islamic Republic.

But tensions between the two countries have escalated in recent months with the United States accusing Iran of trying to build nuclear weapons and of arming anti-U.S. insurgents in Iraq.

Iran says its nuclear ambitions are peaceful but two rounds of U.N. sanctions imposed for continuing atomic work, and the possibility of more on the way, have increased the pressure.

Nine U.S. warships, including two aircraft carriers carrying some 140 aircraft, now patrol waters as close as 35 miles (56 km) from Iran's coast, after crossing the Strait of Hormuz on May 23 in a dramatic daytime display of military muscle.

Iran frequently holds its own war games in the Gulf.

Earlier this year, it test-fired missiles which a commander said could "sink big warships".

Lieutenant Commander Bryce Butler, an officer in charge of monitoring threats to the Nimitz, pointed to a screen showing the carrier passing through a sliver of international waters, hemmed on either side by Iranian waters.

"That's ... only a 20 mile span. That's fairly constrained," he said. "We strive not to transit through those waters."

Regional tensions soared in March when Iran captured 15 British sailors and marines it accused of entering its waters, a charge Britain denied. They were later released.

ANOTHER VINCENNES?

Butler said the strait was tremendously busy, but the chance of another Vincennes was smaller than in 1988, when actual battles between U.S. and Iranian vessels during the latter stages of the Iran-Iraq war meant tensions were at fever pitch.

That contrasts with the contacts these days as the navies try to keep out of each other's way.

"I've noticed more communications and some of that, like this morning, was to reassure us and our escort that they are going to maintain a safe distance. Most of the communications in this region has been with the Iranians," Butler said.

Yet accidents do happen.

Lieutenant Commander Stephen Ures, who pilots a fighter jet and flies missions over Iraq, said his greatest fear was not being shot down but hitting the wrong target in the region of disorienting featureless deserts and hazy skies.

The haze that descends over the Gulf each summer had caused one friend to crash, he said.

Accidents were made more likely by increased air travel, though the navy put massive effort into avoiding them, he said.

"I think the tremendous economic growth of this area has probably made it more likely just for the fact that more people are travelling," Ures said.

"There were some points in history when there was a misunderstanding here and an escalation there, and the next thing you know you've got two sides staring at each other with a hair-trigger. I think it could absolutely happen again, if there was a precipitating incident."

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