The Times cited senior officials as saying the quiet build-up was aimed at reassuring Israel that Washington is serious about addressing Iran's nuclear program and keeping the Straits of Hormuz -- a key oil choke point -- open.

"The message to Iran is, Don't even think about it,'" it quoted a senior Defense Department official as saying.

"Don't even think about closing the strait. We'll clear the mines. Don't even think about sending your fast boats out to harass our vessels or commercial shipping. We'll put them on the bottom of the Gulf."

The Navy has doubled the number of minesweepers in the region, to eight vessels, and stealthy F-22s and older F-15C warplanes have been deployed to regional bases to reinforce existing carrier strike groups, the Times said.

US President Barack Obama has sought to roll back Iran's nuclear program though diplomatic means -- ramping up sanctions to unprecedented levels in recent months -- while not ruling out a military strike.

Western nations and Israel have accused Iran of seeking to develop nuclear weapons under the guise of a civilian uranium enrichment program, charges adamantly denied by Tehran.

Iran and the P5+1 group comprising the five UN Security Council permanent members (Britain, China, France, Russia and the United States) plus Germany plan to hold an experts-level meeting in Istanbul to discuss the dispute.

The talks were to take place between technical experts after three previous rounds earlier this year, at a more senior political level, failed to bridge the vast gap dividing the two sides.

Iran has threatened to close the strategic Strait of Hormuz at the entrance to the oil-rich Gulf if its nuclear program is targeted by air strikes.

That threat, repeated since December, helped propel oil prices to a four-year high of $128 for a barrel of Brent North Sea reference crude in early March.

Foreign ministry spokesman Ramin Mehmanparast told a weekly briefing that, if the powers ignored Iran's nuclear "rights" and failed to bargain on equal terms, the negotiations could lead to an "impasse".

"All that can reinforce the idea that there is a desire to drag out the negotiations or prevent their success," he said.

He also said to reporters after the briefing that "illogical, irresponsible" Western sanctions "amount to a hostile act against Iran and its national interests."

He added: "Iran will do its utmost to defend its national interests and territorial integrity."

Iran and the P5+1 group comprising the five UN Security Council permanent members (Britain, China, France, Russia and the United States) plus Germany were to hold an experts-level meeting in Istanbul to discuss efforts to curb Tehran's atomic activities.

The talks were to take place between technical experts after three previous rounds earlier this year, at a more senior political level, failed to bridge the vast gap dividing the two sides.

Iran is insisting it has a "right" to uranium enrichment under the nuclear Non-Proliferation Treaty, and that that be recognised by the P5+1. It also wants Western sanctions punishing its economy to be eased.

The P5+1 instead is pushing for an immediate end to Iran enriching uranium to 20 percent purity -- just a technical step short of the 90 percent needed to make nuclear bombs -- and to ship out its existing 20-percent stock and close a fortified underground enrichment facility in Fordo.

Mehmanparast said the P5+1's negotiating position and the Western sanctions suggested that maybe the world powers did not want to see the talks bear fruit.

"Many people are starting to conclude that maybe there are specific goals in dragging out the talks and preventing their success. One option is that perhaps there is a link with the US (presidential) election" in November, he said.

He said the "illegal" sanctions contradicted the West's affirmation that it wants to resolve the standoff diplomatically.

He reiterated his government's message that the sanctions would not coerce it into a change of position.