Iranian Foreign Ministry spokesman Ramin Mehman-Parast confirmed receiving a U.S. letter on the Strait of Hormuz, and underlined that Tehran is studying the message and will respond to it if necessary.

Mehman-Parast said the U.S. message was received through three different channels.

"The U.S. Ambassador to the UN Susan Rice had handed a letter to Iran's Ambassador to the UN Mohammad Khazayee; the Swiss Ambassador to Tehran [Livia Leu Agosti] also conveyed the same thing; and Iraqi President Jalal Talabani delivered the same message to Iranian officials," he said.

“Iran is studying the letter and will respond if necessary," Mehman-Parast said, Fars News Agency reported.

Last week, The New York Times, citing unnamed U.S. officials, reported that Washington had used a secret channel to warn Iran's supreme leader Ayatollah Ali Khamenei that closing the narrow strategic waterway would cross a “red line” and provoke a response.

The U.S. officials did not provide details about the covert communication channel, except to say that it was separate from the Swiss government.