On Wednesday, the US Navy said that recovered limpet mine fragments from one of two tanker ships that are believed to have been attacked bore a "striking resemblance" to mines seen during Iranian military parades.
In response, the U.S. military said it did not fly over Iranian airspace.
The Guard's news website, Sepah News, and Iran state news agency IRNA - which called it a "spy" drone - both reported the downing of an RQ-4 Global Hawk in the southern province of Hormozgan on Thursday.
The reported shootdown of the RQ-4 Global Hawk comes after the U.S. military alleged Iran had fired a missile at a drone last week that responded to the attack on two oil tankers near the Gulf of Oman.
RQ-4s typically fly at high altitude to conduct reconnaissance missions.
However, he told The Associated Press: "There was no drone over Iranian territory".
"No US aircraft were operating in Iranian airspace today", Navy Captain Bill Urban, a spokesman for the US military's Central Command, said.
The US has accused Iran of being behind a series of operations against oil tankers in highly sensitive Gulf waters.
Iran claims to have shot down the drone while it was over Iranian territory, however the U.S. has denied any drone was in that airspace.
The Alexandria Ocasio-Cortez concentration camp debate, explained
Well, that went over about as well as you might imagine with conservatives, who went off screaming that the two were not the same. Some also took a dim view of Ocasio-Cortez using the definition "concentration camps".
United Nations report blames Saudi for Khashoggi's murder. What next?
He was asked about his two phones and told to type a message, which he refused to do, the special rapporteur says. Eleven suspects in Khashoggi's killing are on trial in Saudi Arabia; five people face the death penalty. "No.
Trump Believes He Has Authority To Demote Fed Chair Jerome Powell
The US central bank announced it doesn't expect to cut rates this year but did forecast one for 2020. He also recently said he intends to serve his full four-year term, despite Trump's criticism of him.
Two oil tankers were attacked on the strategic Hormuz Strait.
The attacks come against the backdrop of heightened tensions between the US and Iran following President Donald Trump's decision to withdraw from Tehran's nuclear deal a year ago.
Secretary of State Mike Pompeo has blamed Iran for the "blatant assault" on oil tankers in the Gulf of Oman.
President Trump decided a year ago to withdraw America from Iran's nuclear deal with world powers.
The incident is not the first time in recent days that Iran has targeted an American drone off its coast.
However, earlier this week, a spokesman for Iran's atomic energy agency warned that Tehran would surpass limits on its uranium stockpile under the deal and said it was prepared to increase its enrichment to a level just one step short of weapons-grade, which also violates the terms of the agreement.
On Monday, Trump ordered another 1,000 USA troops to the Middle East, which will include a Patriot missile battalion, manned and unmanned surveillance aircraft and "other deterrence capabilities", the Pentagon said. Saudi state media and officials did not immediately report a missile strike Thursday.
"We are closely monitoring the situation and continuing to consult with our partners and allies", Sanders said.
Also, Houthi rebels in Yemen on Wednesday said they hit a Saudi power station with a cruise missile.