Two Iranian fighter jets fired on an unarmed US Predator drone in the Gulf last week but the aircraft was not hit, the Pentagon said Thursday, warning that the United States stood ready to protect its forces in the region.

The incident occurred on November 1 -- less than a week before America's presidential election -- but the Pentagon kept it quiet until now.

"They intercepted the aircraft and fired multiple rounds," spokesman George Little told a news conference.

The SU-25 Frogfoot fighters, much faster than the slow-moving turboprop drone, fired at least twice and made two passes, he said.

It was possible the Iranians intended to warn off the drone but Little said: "Our working assumption is that they fired to take it down."

The confrontation threatened to derail diplomatic efforts to defuse a mounting crisis over Tehran's nuclear program, raising the risk of a potential conflict amid a shadow war of cyberattacks, bombings and assassinations.

Tough new sanctions led by Washington are squeezing Iran's economy while the United States and Israel are accused of staging cyber sabotage on Tehran's uranium enrichment plants.

The US military drone was "never in Iranian air space" and came under fire from Su-25 fighters off the Iranian coast over international waters, Little said.

The robotic Predator aircraft was conducting "routine surveillance" and the United States has told Iran it has no plans to suspend the flights, he said.

"The United States has communicated to the Iranians that we will continue to conduct surveillance flights over international waters over the Arabian Gulf consistent with longstanding practice and our commitment to the security of the region," he said.

In a warning to Tehran, the Pentagon spokesman said the United States was prepared to safeguard its forces.

"We have a wide range of options, from diplomatic to military, to protect our military assets and our forces in the region and will do so when necessary," Little said.

The MQ-1 drone was pursued further by the Iranian warplanes but was not fired on again, he said.

The Predator returned safely to an unspecified military base in the region following the incident that occurred at 4:50 am US eastern standard time (0850 GMT).

The Predator was intercepted about 16 nautical miles off the Iranian coast, beyond the Islamic Republic's territorial waters that extend 12 nautical miles off the country's shore.

Iranian military speedboats have sometimes swarmed US warships in the Gulf and the strategic Strait of Hormuz, a vital waterway for the world's oil, but the incident last week was the first involving an American drone in a confrontation with Iranian aircraft, officials said.

Tensions over Iran's nuclear ambitions prompted the United States to bolster its military presence around the Gulf over the past year, deploying two aircraft carrier battle groups in the area at all times, a squadron of stealthy F-22 fighters to the United Arab Emirates and more minesweeper ships.

With America's drawn out election campaign finally over, analysts had predicted President Barack Obama might have more leeway to pursue diplomacy with Iran. But the encounter with the Iranian fighter jets could complicate any attempt for a deal.

A new round of talks between Iran and six world powers, the first since June, is expected by the end of the year or in early 2013.

Iran insists its nuclear program is peaceful and has made clear any deal with the major powers has to offer relief from crippling sanctions.

At the State Department, officials on Thursday unveiled yet more sanctions on Iran, targeting the communications minister and the culture ministry among others for censoring the media and the Internet.

The move against Communications Minister Reza Taghipour came after he was blamed for ordering the jamming of international satellite TV broadcasts and restricting Internet access, a State Department official said.

The United States is determined to stop the "Iranian government from creating an 'electronic curtain' to cut Iranian citizens off from the rest of the world," said State Department spokeswoman Victoria Nuland.