The US military has said a missing unmanned spyplane was involved in a joint CIA military operation on Afghanistan's border with Iran.
The Pentagon has admitted the RQ 170 Sentinel drone is lost somewhere in Iran.
But the US disputes Iranian claims to have shot down the state-of-the-art spy aircraft.
News of the CIA involvement is causing controversy in Washington.
Congressman Dennis Kucinich told Sky News the involvement of America's spy agency was a worrying development.
"We have to be very careful that we don't stumble into a wider war here. If we are in Iran's airpace with anything that belongs to the US, that's a provocation," he said.
The revelation coincides with speculation a covert war is being waged in Iran by America and Israel to thwart Iranian nuclear ambitions.
A series of events remain unexplained. Iranian scientists have been assassinated, in one case by a bomb strapped to his vehicle by a hit team on a motorbike.
A huge explosion at a top secret missile base in the Iranian desert appears to have killed the lead scientist on missile development.
Mr Kucinich said he is worried these events mean the region is sliding towards greater conflict.
"The events have been confirmed, so when you start to connect the dots, those dots start to spell the word war," he said.
The US has justified the use of drones in Afghan airspace as necessary to keep watch over American forces, but CIA involvement seems to confirm their use to gather intelligence beyond the border with Iran.
The Sentinel drone, thought to be 65ft in wingspan, is one of the world's most secret aircraft. Packed with surveillance electronics, it is capable of staying in the air for days.