(CNN) -- The U.S. military reported Monday on a "significant" confrontation involving five Iranian Revolutionary Guard boats that "harassed and provoked" three U.S. naval ships in international waters over the weekend.

U.S. military officials said the incident occurred early Sunday morning in the Strait of Hormuz, a narrow shipping channel leading in and out of the Persian Gulf.

The five Iranian ships made "threatening" moves -- in one case coming within 200 yards of a U.S. ship, the U.S. officials said.

In one radio transmission, the Iranians told the U.S. Navy: "I am coming at you. You will explode in a couple of minutes," the U.S. military officials told CNN.

When the U.S. ships heard that radio transmission, they took up their gun positions and officers were "in the process" of giving the order to fire when the Iranians abruptly turned away, the U.S. officials said. Video Watch what U.S. officials are saying about the incident »

After the radio transmission, one of the Iranian ships dropped white boxes into the water in front of the U.S. ships, the officials told CNN. It was not clear what was in the boxes, the officials said. See a map of the Strait of Hormuz »

No shots were fired and no one was injured in the confrontation.
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The Iranian government had no immediate response to the Sunday incident.

The Strait of Hormuz, which is in international waters, is near much of the world's oil supplies.

The White House urged Iran to refrain from "such provocative actions that could lead to a dangerous incident in the future," National Security Council spokesman Gordon Johndroe said.

In November, the U.S. military reported that Iran's Revolutionary Guard Corps had taken command of that country's naval operations in the Persian Gulf.

The U.S. considers the Revolutionary Guard to be a major supporter of terrorist activity.

Tensions between Iran and the U.S. have increased over the last few years. The U.S. has concerns about Iran's nuclear program, and has charged that Iran supplies weapons to insurgents in Iraq who target American forces.

In March, Iran detained 15 crew members of a British ship before releasing them after nearly two weeks. Iran claimed the British vessel strayed into Iranian waters -- a claim Britain strongly denied.