Two Russian-made Iranian Su-25 fighter jets fired upon an unarmed U.S. Air Force Predator drone over the Persian Gulf last week, CNN reported Thursday.

Pentagon officials confirmed the incident but said the drone was in international airspace east of Kuwait and was conducting routine maritime surveillance.


While the drone was not hit, the incident raises grave concerns over Iranian military action in the vital oil-exporting area. The jets were part of Iran's Revolutionary Guard Corps force, CNN reported, citing unidentified U.S. officials.


The unprecedented incident occurred on Nov. 1, just a few days before the presidential election. The Obama administration did not publicly reveal the incident at that time. Nonetheless, Washington has protested to Iran through diplomatic channels over the firing, but has heard no response.


"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," Pentagon spokesman George Little told a briefing on Thursday, according to Reuters.


"We have a wide range of options from diplomatic to military to protect our military assets and our forces ... and will do so when necessary.”


Little added: "Our aircraft was never in Iranian airspace. It was always flying in international air space. The internationally recognized territorial limit is 12 nautical miles off the coast and we never entered the 12 nautical mile limit."


According to Little, “Our working assumption is that they fired to take it down,You’ll have to ask the Iranians why they engaged in this action.”


The incident occurs during a time of heightened tensions as Iran has been hit with economic sanctions in an effort to halt their nuclear program. Iran has threatened to close the Strait of Hormuz in retaliation. A new round of economic sanctions were announced on Thursday against Iran. The new sanctions are due to the "Iranian government's human rights abuses, its support of terrorism and Iran's Islamic Revolutionary Guard Corps," reports Fox News.


Last year, a CIA drone crashed in Iran, likely providing Tehran with sensitive U.S. technology.