Iran stepped up its crackdown on Monday after recent protests, making more arrests while holding the door open to Washington for further nuclear negotiations.

The arrests – including that of Javad Emam, the spokesperson for the main reformist coalition – came after Iranian and US officials held talks in Oman that both sides painted as positive.

On Saturday, Iran heaped more jail time on Nobel Peace Prize winner Narges Mohammadi, and on Monday arrested Hossein Karoubi, the son of prominent dissident Mehdi Karoubi.

Weeks after repressing a wave of protests, one of the greatest challenges to the government since it came to power in the 1979 Islamic revolution, Tehran has taken a two-track approach.

It is rounding up and jailing perceived critics, while at the same time pursuing a potential diplomatic opening with US President Donald Trump's administration.

A spokesperson for the Reformist Front coalition told local media on Monday that Iran's Revolutionary Guards had arrested the group's spokesman Emam.

Emam was one of at least five Reformist Front figures to be detained, as were several activists and filmmakers who co-signed a protest statement.

Iran's government has branded the protests "riots" fuelled by its arch-foes Israel and the US.