WASHINGTON - Eleven vessels from Iran's Islamic Revolutionary Guard Corps Navy (IRGCN) came dangerously close to U.S. Navy and Coast Guard ships in the Persian Gulf, the U.S. military said on Wednesday, calling the moves "dangerous and provocative."

While such interactions had occurred occasionally a few years ago, they had stopped in recent years, and this incident came at a time of increased tensions between the two countries.

According to the statement, the Iranian vessels approached six U.S. military ships while they were conducting integration operations with Army helicopters in international waters.

At one point, the Iranian vessels came within 10 yards of the U.S. Coast Guard cutter Maui.

The U.S. ships issued several warnings through bridge-to-bridge radio, blasts from the ships' horns and long-range acoustic noisemaker devices.

The Iranian ships left after about an hour, the statement added.

There was no mention of the incident in Iranian media.

"The IRGCN's dangerous and provocative actions increased the risk of miscalculation and collision, [and] were not in accordance with the internationally recognized Convention on the International Regulations for Preventing Collisions at Sea," the U.S. military's statement said.

Tensions between Iran and the United States increased earlier this year after the United States killed Qassem Soleimani, the head of Iran’s elite Quds Force, in a drone strike in Iraq.

Iran retaliated on January 8 with a rocket attack on Iraq’s Ain al-Asad base where U.S. forces were stationed. No U.S. troops were killed or faced immediate bodily injury, but more than 100 were later diagnosed with traumatic brain injuries.

Earlier this month President Donald Trump said that Iran or its proxies planned a sneak attack on U.S. targets in Iraq, and warned they would pay a "very heavy price."

Maritime security sources said on Wednesday that a Hong Kong-flagged tanker was briefly detained in Iran after armed Iranian guards in speedboats directed the vessel into its waters while it was sailing through the Gulf of Oman.

The sources said the SC Taipei chemical tanker had been sailing in international waters on Tuesday when it was stopped.