The Obama administration has used a secret channel of communication to warn Ayatollah Ali Khamenei, Iran's supreme leader, not to make good on the country's threat to close the Strait of Hormuz, the New York Times reported on Friday.

Government officials were quoted as saying that closing the strait is a "red line" that would provoke an American response. But they declined to describe the unusual contact between the two governments, and whether there had been an Iranian reply.

The secret channel was used to underscore privately to Iran " the depth of American concern" about rising tensions over the strait, a strategically crucial waterway connecting the Persian Gulf to the Gulf of Oman, where 16 million barrels of oil -- about a fifth of the world's daily oil trade -- flow through every day, the report said.

Iran's threat to close the strait came in late December in response to the planned expanded sanctions by the West to target its oil exports over its controversial nuclear program.

Senior Obama administration officials have said publicly that Iran would cross a "red line" if it does so. However, American naval officials said their biggest fear is that an overzealous naval captain of Iran's elite Islamic Revolutionary Guard could do something provocative on his own, setting off a larger crisis.

Some officials and analysts described Iran's threat as bluster and an attempt to drive up oil price.

"Blocking the route for the vast majority of Iran's petroleum exports -- and for its food and consumer imports -- would amount to economic suicide," the New York Times report said.