An official from the European Union's naval mission "Aspides" told Reuters that the ships had received VHF transmissions from the Iranian Revolutionary Guard, saying that "no ship is allowed to pass through the Strait of Hormuz".
The Strait is the world's most important oil export route, connecting the largest oil producers in the Persian Gulf, such as Saudi Arabia, Iran, Iraq and the United Arab Emirates, with the Gulf of Oman and the Arabian Sea, news.bg recalls.
The official, who spoke to Reuters on condition of anonymity, said that Iran had not officially confirmed such an order.
Tehran has for years threatened to block the narrow waterway in retaliation for any attack on the ayatollahs' regime.
The United States "has the best-trained and most lethal force in the world and will continue to operate with the highest levels of professionalism and adhere to international norms. Iran's Islamic Revolutionary Guard Corps must do the same," CENTCOM stressed.
The Strait of Hormuz between Iran and Oman is 55 kilometers wide, DPA notes.