The U.S. military on Wednesday denounced what it described as provocative maneuvers by Iranian vessels near American naval and Coast Guard ships in the Persian Gulf.

In a statement, U.S. Naval Forces Central Command said 11 small vessels belonging to Iran’s Revolutionary Guard Corps Navy conducted “dangerous and harassing approaches” toward a fleet of American ships, including the USS Lewis B. Puller, an expeditionary mobile base vehicle, and the USS Paul Hamilton, a destroyer.

The American ships were carrying out operations with Army Apache helicopters in the northern Gulf, the statement said.

The Iranian vessels “repeatedly crossed the bows and sterns of the U.S. vessels at extremely close range and high speeds, including multiple crossings of the Puller with a 50 yard closest point of approach and within 10 yards” of a Coast Guard ship’s bow, according to the military.

The American ships transmitted radio warnings and made warning sounds with no initial response. An hour later, the Iranian vessels responded and fell back, the military said.

Iran’s “dangerous and provocative actions increased the risk of miscalculation and collision, were not in accordance with the internationally recognized . . . ‘rules of the road’ or internationally recognized maritime customs, and were not in accordance with the obligation under international law to act with due regard for the safety of other vessels in the area,” the statement said.

The Trump administration has had a series of military clashes with Iran and affiliated groups over the past year, including Iran’s downing of an American drone and its launch of ballistic missiles at facilities housing U.S. personnel in Iraq. The United States, meanwhile, conducted a drone strike in January that killed Qasem Soleimani, Iran’s top military commander, in Baghdad and has attacked Iranian-linked militias in Iraq.

Such encounters at sea have been common at different points in recent years, with naval officials sometimes classifying such approaches as “unsafe and unprofessional.”