A few hundred diehard Iranian conservatives rallied on Monday against Israel and said US President Donald Trump had hastened its demise with his decision to recognise Jerusalem as its capital.

The rally in downtown Tehran featured the sort of thumping, Turkish-style dance music that is normally banned in Iran but has become increasing popular at hardliner events.

It is made acceptable to conservative ears with the addition of lyrics such as "the US is a murderer" and "Palestinian mothers are losing their children" and, of course, the ubiquitous "Death to America".

Participants blamed the middling turnout on rushed preparations.

"The publicity was a bit weak. I only learned about today's demo around midnight, and I'm coming directly from the hospital because I'm a medical student," said Ali Esfahani, 23.

He said Trump's decision to move the American embassy to Jerusalem, which was widely condemned across the globe, "was one more cruelty on top of America's previous oppressions" and could not be tolerated.

Such protests tread a fine line, pledging support for the Palestinian cause without calling for direct military action by Iran.

"I don't think there will be a need to send any troops because there are a lot of people in Lebanon, Syria and inside the Palestinian Territories. They will be enough to get rid of the Israelis," a cleric, Seyed Abdullah Hosseini, told AFP.

A neon board on the side of the square announced that there were only 8,240 days left for Israel -- a reference to a speech by supreme leader Ayatollah Ali Khamenei in which he predicted the end of Israel by 2030.

"Mr Trump has done a good job of speeding things up. We were expecting Israel to be dismantled later... but this is the beginning of the end of Israel," said Hosseini.