Iran's president has said that the Islamic Republic will soon announce "very important" achievements in the nuclear field, during an address to crowds celebrating the anniversary of the country's 1979 revolution.

Ahmadinejad addressed tens of thousands of supporters in Tehran's Azadi [Freedom] Square on Saturday as Iranians across the country joined state-organised rallies to mark the occasion.

"In the coming days the world will witness Iran's announcement of its very important and very major nuclear achievements," Ahmadinejad told the crowd in a speech relayed live on state television. He gave no further details. 

The president spoke from a stage in front of which a full-scale model of a captured US spy drone was erected, which Iranian officials said they brought down by hacking its flight controls as it overflew their territory in December on a surveillance mission.