Report: U.S. Warned Khamenei over Blocking Hormuz

The United States has used a secret channel to warn Iran's leaders against closing the strategic Strait of Hormuz, saying that doing so would provoke a U.S. response, the New York Times reported.

Iran has threatened to close the narrow and strategic waterway -- a chokepoint for one fifth of the world's traded oil -- in the event of a military strike or the severe tightening of international sanctions.

The New York Times, citing unnamed U.S. officials, said late Thursday that the White House has communicated to Iran's Supreme Leader Ayatollah Ali Khamenei that closing the strait would be a "red line" and provoke a response.

The officials did not provide further details about the covert communication channel, except to say that it was separate from the Swiss government, through which the United States occasionally relays messages to Iran's leaders.

The United States and its allies have stepped up increasingly harsh sanctions on Iran over its nuclear enrichment program, which they have charged is part of a secret drive to develop nuclear weapons.

Iran has insisted its nuclear program is entirely peaceful and vowed to retaliate against any strike on its facilities.

Tensions have flared in recent days following the killing of an Iranian nuclear scientist in a bombing Tehran has blamed on U.S. and Israeli intelligence services. U.S. officials have denied any involvement in the attack.

Iran's Revolutionary Guards have announced new naval maneuvers in the Strait of Hormuz within the next few weeks, underlining Tehran's threat to close the narrow channel between the Persian Gulf and the Arabian Sea.

Washington has meanwhile sent a second aircraft carrier to waters just outside the Gulf, and a third is on its way.