Iran has claimed its Revolutionary Guard have shot down a US drone amid heightened tensions between the two countries.
US military leaders are yet to comment on the alleged attack that the middle eastern country's state news says happened in its airspace.
The drone is said to have been a RQ-4 Global Hawk and was downed in the south of the country.
The news comes after the Pentagon accused Iran of trying to shoot down a Reaper drone as it flew over the Gulf of Oman last week.
Lt. Col. Earl Brown claimed Iranian authorities tried to use a surface-to-air missile to hit the MQ-9 drone.
The drone was flying over one of two crippled tankers in the gulf that the US publicly blamed on Iran.
The outgoing Secretary of Defence Patrick Shanahan announced the deployment of 1,000 more US troops to the region in response to "hostile behaviour".
"I have authorised approximately 1,000 additional troops for defensive purposes to address air, naval, and ground-based threats in the Middle East," Shanahan said in a statement.
"The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behaviour by Iranian forces and their proxy groups that threaten United States personnel and interests across the region."
The deployment comes after a similar deployment of 1,500 U.S. troops occurred in late May.
Iran and its backers in Russia have accused the White House of unnecessarily increasing tensions in the region, starting with Donald Trump's decision to unilaterally pull the U.S. out of the international nuclear agreement with Iran and ratcheting up economic sanctions and blacklisting its state institutions.
Iranian President Hassan Rouhani responded saying he would not "wage war against any nation", but his country is united against the U.S.
"Iran will not wage war against any nation," he said.
"Despite all of the Americans' efforts in the region and their desire to cut off our ties with all of the world and their desire to keep Iran secluded, they have been unsuccessful.