Tehran: A senior commander of Iran's elite Revolutionary Guard says his country will not return a US surveillance drone captured by its armed forces.

Deputy head of the Guard General Hossein Salami said on Sunday in remarks broadcast on state television that the violation of Iran's airspace by the US drone is a "hostile act" and warned of a "bigger" response.

But he didn't elaborate on what Iran might do.

Iranian television broadcast video Thursday of Iranian military officials inspecting what it identified as the RQ-170 Sentinel drone, and offered the first evidence that Tehran had captured the aircraft.

Iranian state radio has said the unmanned aircraft was detected over the eastern town of Kashmar, some 225 kilometres from the border with Afghanistan.

US officials have acknowledged losing the drone.