US Defence Secretary Donald Rumsfeld has denied he authorised military overflights in Iran for surveillance on the country's alleged nuclear programme, Xinhua reported.
"I checked and I know we had no US aircraft doing what ... Iran is saying," Rumsfeld told a television's programme on Sunday.
"What investigations we've been able to undertake have suggested that the charge was false," he said.
"It may very well have been Iranian air activity in that country by elements of the government that were not coordinating with other elements of the Iranian government".
The defence chief rejected recent US reports that said US surveillance planes have been overflying Iran since April 2004, spying on its nuclear programme and probing for weaknesses in its air defence.
In February, the Washington Post quoted US officials as saying that small, pilotless planes penetrated Iranian airspace from US military facilities in Iraq, trying to pick up traces of nuclear activity to gather information that was not accessible by satellites.
When pressed about whether any US intelligence agencies might have organised such flights, Rumsfeld did not rule out the possibility: "I can't speak for intelligence agencies, but not to my knowledge".
Rumsfeld also denied knowledge about reports that Iran had protested to the US about reconnaissance flights on its territory and that the protest was forwarded to the Pentagon.
The reported spy flights have raised concerns about US military preparations for possible attacks on suspected Iranian nuclear sites.
US officials have declined to rule out a military option but have indicated they are giving international diplomatic efforts a try.