The Bahrain-based US Fifth Fleet warned Iran that any attempt to close the Strait of Hormuz will "not be tolerated."
"The free flow of through the Strait of Hormuz is vital to regional and ," the fleet said in a statement released to Reuters.
"Anyone who threatens to disrupt freedom of navigation in an international strait is clearly outside the community of nations; any disruption will not be tolerated," the statement added.
The statement came after Iran threatened to stop ships moving through the strategic oil route as a part of a "military drill."
Last week Iranian parliament member Parviz Sarvari told an Iranian media outlet that “soon we will hold a military maneuver on how to close the Strait of Hormuz. If the world wants to make the region insecure, we will make the world insecure.”
The threat was repeated by Iran's chief naval officer on Tuesday.
Asked whether the Fifth Fleet would take specific measures in response to Iran's threat to close the Strait, the fleet said it "maintains a robust presence in the region to deter or destabilizing activities," without providing further detail.
However, United States has long maintained any attempt to close the Strait of Hormuz would be regarded as "an act of war."
Concerns Iran might move to close the strategically vital Strait - through which 40% of the world's oil supplies flow - began to mount after students in Tehran sacked the British embassy earlier this year.
Western officials, who said Tehran had prompted the violent demolition as a "dramatic piece of political theater." Britain, France, and the Netherlands closed their embassies in Iran and ejected Tehran's envoys from their capitals.
Several other European nations – including Italy and Germany – censured Iran for the incident.
The incident also prompted a new, more stringent round of sanctions from the European Union and United States targeting Iran.