Iran's supreme leader Ayatollah Ali Khamenei Wednesday dubbed some US officials "first-class idiots" as he ridiculed them for predicting the collapse of the Islamic Republic. 

"Some US officials pretend that they are mad. Of course I don't agree with that, but they are first-class idiots," he said in speech in Tehran, quoted on his official Twitter feed.

Khamenei was having a dig at US officials who had predicted there would be regime change in Iran by the end of 2018. 

"A while ago, a US politician had said, among a gathering of terrorists and thugs, that he hopes to celebrate this Christmas in Tehran," Khamenei said, according to his Twitter feed. 

"Christmas was a few days ago. This is how US calculations work."

It was not clear to which US official he was referring, but members of President Donald Trump's administration have called for regime change and predicted it would happen soon.

This has included National Security Advisor John Bolton -- a long-time regime change advocate -- who often speaks at gatherings of the exiled People's Mujahedeen of Iran (MEK) opposition group, considered a terrorist cult by Tehran's leaders. 

"Before 2019 we here will celebrate in Tehran," Bolton told an MEK meeting in Paris in July 2017.