The United States and Britain will not tolerate Iranian attempts to block the strategically important Strait of Hormuz, defense chiefs from the two Western powers said Wednesday.

US Defense Secretary Leon Panetta and his counterpart Philip Hammond spoke about Iran's "destabilizing behavior" during a bilateral meeting, Panetta told reporters at a joint news conference.

"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," the Pentagon chief said.

"And the United States is fully prepared for all contingencies here."

He said Washington has "invested in capabilities 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."

Fears of a closure of the Strait of Hormuz -- through which about a fifth of the world's traded oil passes -- intensified earlier this year after Iran threatened to close it if Western governments kept up efforts to rein in Tehran's controversial nuclear program by choking off its oil exports.

In response, the US military has beefed up its presence in the region.

It has deployed the USS Ponce amphibious transport dock, increased the number of minesweepers in the Gulf and sent in MH-53 Sea Stallion anti-mine transport helicopters, as well as underwater drones.

Amid tensions over Iran and Syria, it has also brought forward the deployment of the USS John Stennis aircraft carrier to the region to shorten the time when a sole carrier is in the region.

Hammond said London was "determined" to work as part of the international community effort on the matter.

"I can reaffirm our commitment to play our part in maintaining freedom of navigation in the international waters of the Gulf and the Strait of Hormuz," he said.

"Any attempt by Iran to close the strait would be illegal and the international community will not allow it to happen."

On Tuesday, the Pentagon announced that a multinational anti-mine operation would take place near the Gulf in September. Tehran reacted by scoffing at the announcement.

"The Americans boast a lot about many things, but they are facing problems in practice," General Mahmoud Fahimi, deputy chief of the naval forces of Iran's Revolutionary Guards, told the Fars news agency.