Investing.com -- The United Arab Emirates issued a missile threat warning on Monday, marking the first such alert since a ceasefire between the US and Iran began approximately one month ago.

The warning followed an earlier incident in which an oil tanker owned by Abu Dhabi National Oil Co. was struck by Iranian drones outside the Strait of Hormuz. The strait previously handled about one-fifth of global oil and liquefied natural gas transit before conflict erupted in late February.

President Donald Trump announced Sunday plans to restore transit through the waterway and assist stranded vessels in exiting the Persian Gulf. The operation began Monday with US military support, including guided-missile destroyers, aircraft and drones. Two US-flagged merchant ships have transited the strait, according to the US military.

Iran stated it would attack US forces if they enter Hormuz. Iran's semi-official Fars news agency reported that the country's military fired warning shots at US Navy ships attempting to approach the Strait of Hormuz, using cruise missiles, rockets and combat drones.

Brent crude traded 2.5% higher at just under $111 a barrel following the escalation.

The ceasefire, which took hold about a month ago, has been part of diplomatic efforts to end a war that has resulted in thousands of deaths and disrupted global energy supplies.