Iranian media reported that their country's military had shot down a US reconnaissance drone in eastern Iran, but a US official said there was no indication the aircraft had been shot down.
US Secretary of State Hillary Clinton implicitly defended Washington's use of drone strikes to kill suspected militants, just days after one of the aircraft killed one of al Qaeda's most powerful figures in Pakistan.
Iran said it had captured a US intelligence drone in its airspace over the Gulf in the last few days, but the US military quickly denied having lost any unmanned aircraft in the Middle East.
A US drone strike killed at least 10 people suspected to be Taliban fighters in Pakistan's northern tribal areas, intelligence sources said, days after another drone strike killed a top militant leader in the area.
Iran's Revolutionary Guards said they had conducted tests aimed at bringing down a "hypothetical" foreign surveillance drone during a military exercise, the official Fars news agency said.