US Secretary of Defense Leon Panetta said Wednesday vowed Washington will not allow Iran to close the strategically vital Strait of Hormuz.

Iran’s leaders have threatened to close the Strait – through which one-fifth of the world's oil exports flow – unless sanctions against their critical oil shipments are lifted.

Panetta said the “Iranians need to understand that the United States and the international community are going to hold them directly responsible for any disruption of shipping in that region by Iran or, for that matter, by its surrogates.”

He added, “The United States is fully prepared for all contingencies,” and warned that Tehran would be “completely defeated” should it test Washington's military might.

The US has invested in capabilities in the region to “ensure that the Iranian attempt to close down shipping in the Gulf is something that we are going to be able to defeat if they make that decision to do that,” Panetta said.

Panetta’s comments came on the heels of the Pentagon’s announcement that the US Navy would accelerate the deployment of the USS John Stennis carrier group to the Gulf region. The move comes in order to allow the US to maintain a two-carrier presence in the area through the end of the year.

However, Pentagon Press Secretary George Little denied that the accelerated deployment of the Stennis was a direct response to tensions with Iran.

“This is not a decision based solely on the challenges posed by Iran,” Little said on Monday, adding that the deployment of the Stennis is not intended to send a signal to Iran.